The clearest deterioration occurred after foam had remained on epithelial-cell traces for 25 hours, while complete blood and saliva profiles remained obtainable even after longer exposure. Because the experiment did not reproduce an actual fire, it did not test the effects of intense heat, smoke or soot on burned surfaces. The investigation addressed a recurring problem in forensic genetics: biological traces may be recovered from a vehicle or crime scene after an extinguisher has been used, yet genetic analysis can fail to identify the person who deposited the material.

Vehicles involved in theft, hit-and-run collisions or other criminal activity may be burned, and extinguishers are also sometimes applied without a fire in an attempt to conceal evidence. DNA from occupants can help identify a driver or passenger, making the reliability of post-extinguisher analysis important for investigations. The study was published as a short communication in the International Journal of Legal Medicine on 20 October 2026.

For the experiment, the team prepared blood, saliva and epithelial-cell samples and deposited them on a laboratory bench, steering wheel, car door, seat-belt buckle and glove-compartment cover. Blood and saliva were applied in different volumes, while epithelial touch traces were created by rubbing fingers and hands onto the surfaces, either as single-donor deposits or mixtures from two people. The overall sample collection involved three female employees aged 26 to 59 whose DNA profiles were known.

For the touch-trace procedures, one woman classified as a “good shedder” was selected alongside another classified as a “bad shedder,” so the experiments represented both stronger and weaker cell transfer. All surfaces were cleaned before use, and negative controls produced no profiles. Each trace was allowed to dry for 24 hours.

Some samples were then sprayed on all sides until one of three commercial extinguishers was empty: 6 liters from the powder or foam extinguisher and 2 liters of carbon dioxide. Samples were collected one hour later, with additional 25-hour cohorts prepared for the powder and foam agents. Untreated samples served as controls.

The carbon dioxide group was sampled only after one hour because the gas dissipates rapidly and leaves no residue, meaning that prolonged exposure was not considered relevant in the experimental setup. The powder and foam cohorts included 196 samples each, comprising 72 blood traces, 72 saliva traces and 52 epithelial-cell traces; the carbon dioxide cohort contained 98 samples, while 130 untreated samples formed the reference group. The powder was an ABC formulation intended for fires involving solids, liquids or gases.

Its main components included ammonium dihydrogen phosphate, ammonium sulfate, barium sulfate and silica gel. The foam, recommended for solid and liquid fires, contained alkyl polyglucosides, 2-(2-butoxyethoxy)ethanol, ethanol and a perfluorinated amphoteric surfactant. The carbon dioxide extinguisher displaced oxygen without leaving a chemical residue.

This difference in composition and persistence was central to the results: powder and foam remained on the sampled surfaces, whereas carbon dioxide rapidly escaped. The investigators also noted that the agents did not cause extensive mechanical removal of traces, such as the washing or blowing away expected if powerful water flow had been applied. DNA was extracted with forensic casework kits and quantified by real-time PCR.

Two microliters of each extract were analyzed in duplicate and amplified with the PowerPlex ESX17fast multiplex kit. Fragment results were examined on an ABI 3500 genetic analyzer. A full profile contained every allele attributable to the known donor at all tested STR loci.

A partial profile lacked one to four donor alleles, while a “no evidence” profile lacked more than four and could not identify the donor. The quantification system had a reproducible detection threshold of at least 25 picograms of DNA. Previous validation work cited by the researchers found that complete ESX17fast profiles remained possible with inputs of approximately 62.5 to 64 picograms, and that partial profiles commonly occurred at still lower template amounts.

After one hour, none of the three extinguishers caused a general decrease in DNA concentration compared with controls. The measured concentrations covered a broad range because the samples differed greatly in biological content: control blood on the laboratory bench reached 10.2 nanograms per microliter, while epithelial deposits from two people measured below 0.001 nanogram per microliter. Among treated samples, the highest concentration was 10.7 nanograms per microliter in a 20-microliter blood sample on artificial leather one hour after foam treatment.

Foam reduced average measured DNA by about 40% after 25 hours, with exceptions for 25-microliter saliva samples and epithelial traces from two people. The untreated controls showed no corresponding decline. The investigators attributed the foam-associated reduction cautiously to its perfluorinated surfactant and cited prior evidence that such compounds can increase reactive oxygen species and promote DNA damage.

Apparent increases in some later measurements were more plausibly related to variation in the starting material than to an extinguishing agent. Contact pressure, the duration of contact, the random number of cells transferred, time since eating or drinking, and an individual’s shedding status can all affect initial DNA yield. This variability also produced large standard deviations in some control measurements, including plus or minus 3.2 nanograms per microliter for 20-microliter blood samples.

The authors therefore emphasized the broader pattern across cohorts rather than isolated differences in mean concentrations. Their results indicate that the agents did not uniformly destroy or remove quantifiable DNA during the tested exposure periods. STR results showed that the chemical agents did not generally make profiling impossible.

All untreated blood samples produced full profiles. At 25 hours, the rates remained 100% for powder and 95% for foam. Saliva showed a similar pattern: after one hour, full profiles ranged from 94% with foam to 98% with carbon dioxide, and after 25 hours they ranged from 95% with foam to 100% with powder.

Even when foam lowered measured DNA concentration, enough material remained for successful amplification. The researchers linked this outcome to the comparatively generous input available for amplification and to validation results showing that complete profiles can be obtained with relatively small DNA quantities. Touch DNA produced more variable outcomes, reflecting the inherently low DNA content of epithelial-cell deposits.

Untreated samples yielded complete profiles in 28% of cases after one hour and 67% after 25 hours; at one hour, 39% were partial and 33% contained insufficient donor information. Following treatment, complete profile rates were 31% for powder, 18% for foam and 46% for carbon dioxide after one hour. At 25 hours, 25% of powder samples and 3% of foam samples produced complete profiles, while 17% and 15%, respectively, were partial.

Compared with the respective one-hour results, the proportion of full profiles fell by 6 percentage points for powder and 15 points for foam, while no-evidence results rose by 17 and 13 points. Epithelial traces are difficult because keratinized cells contain little intact nuclear DNA, so their baseline limitations were often greater than the added effect of the extinguishers. The results support a narrow conclusion: extinguishing-agent residue alone is unlikely to defeat forensic DNA analysis, especially when investigators recover blood or saliva from surfaces that were not directly burned.

The authors noted that heat in a real fire causes DNA fragmentation and makes amplification more difficult, while smoke and soot may also affect trace quality. They described the experiment as a mock scenario rather than a model of a fire scene and noted that successful identification from heavily burned surfaces would be unlikely regardless of whether an extinguisher had been used. Real cases may also remain in the laboratory for much longer before sampling.

The researchers called for future work to incorporate actual fire exposure, longer incubation with extinguishing agents and the delays encountered during real forensic processing.

Subject of Research: Effects of powder, foam and carbon dioxide fire extinguishers on forensic DNA quantity and STR-profile integrity

Article Title: Impact of fire extinguishing agents on DNA quantity and integrity

Article References: Konrad, H., Fertyk, S., Firl, K., Hartung, B., & Poetsch, M. (2026). Impact of fire extinguishing agents on DNA quantity and integrity. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04042-2

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04042-2

Keywords: forensic DNA, fire extinguishers, STR profiling, touch DNA, blood evidence, saliva evidence, ABC powder, firefighting foam, PFAS, crime scenes, Impact, fire

The logic is disarmingly simple. Every cell in a mixture belongs to one person, so if investigators can physically isolate individual cells before DNA analysis, each isolated cell yields a single-source profile rather than a tangled blend. The idea is not entirely new—researchers first demonstrated DNA fingerprinting from single cells in 1997, when a team at the University of Leeds amplified DNA from a single cell and produced a usable genetic profile. What has changed is the sophistication of the isolation tools, the integration of genotype data across many cells, and the emergence of probabilistic frameworks that can turn a handful of single-cell profiles into courtroom-grade evidence. The Sichuan University review, published in October 2026, systematically evaluates these advances and charts a path toward routine forensic application.

The first family of techniques the authors examine is micromanipulation and laser capture microdissection, or LCM. Micromanipulation is the most direct approach: an operator uses a fine glass capillary under a microscope to pick out target cells one by one, a method first applied to forensic identification in sexual assault cases as early as 2008, when researchers isolated single sperm cells by micromanipulation for human identification. LCM takes a more automated approach, using a laser to cut target cells directly from a stained slide while leaving unwanted cells behind. The technique was originally developed at the National Institutes of Health in the late 1990s to open the microscopic frontier to molecular analysis, and forensic scientists quickly adapted it to separate pure spermatozoa from epithelial cells for short tandem repeat, or STR, analysis. Studies published in 2006 and later confirmed that laser microdissection could recover clean sperm profiles from sexual assault swabs, and more recent work has refined the hardware itself, including systems based on structured light modulation with dual cutting modes and negative pressure adsorption collection. The strength of these approaches is precision: the operator sees exactly which cell is being taken. The weakness is throughput, because isolating enough cells for a robust profile remains slow and labor-intensive.

The second category pairs fluorescence-activated cell sorting, known as FACS, with imaging flow cytometry, or IFC. Flow cytometry separates cells based on measurable properties: sperm cells, for example, are haploid while vaginal epithelial cells are diploid, and cells can also be distinguished by surface markers such as CD45, cytokeratin, and MHC class I expression. Researchers demonstrated sperm and vaginal cell separation by flow cytometry for DNA typing after sexual assault as early as 1999, and subsequent work extended the approach to fluorescence- and magnetic-activated cell sorting strategies for separating spermatozoa from multi-contributor biological mixtures. Imaging flow cytometry adds a crucial forensic capability: it captures high-resolution images of every cell as it flows past the detector, allowing classification based on morphological characteristics. A 2024 study showed that imaging flow cytometry could classify epidermal, buccal, penile, and vaginal epithelial cells using morphological features alone—a breakthrough for touch DNA cases, where the mixture often involves the same cell type from multiple people and where traditional separation methods fail entirely. FACS offers far higher throughput than micromanipulation, but it requires the sample to be in single-cell suspension, which means solid tissues and sticky stains must first be dissociated, a step that can damage fragile forensic material.

The third and arguably most promising category is microfluidic-based systems, represented by the DEPArray platform. This technology uses dielectrophoresis—the movement of cells in non-uniform electric fields—to trap individual cells in electronically controlled cages within a microfluidic cartridge. Operators can then image each trapped cell and selectively release only the cells of interest, achieving a digital precision that earlier methods could not match. Studies published in 2017 demonstrated the isolation and genetic analysis of pure cells from forensic biological mixtures with this approach, and subsequent research showed enhanced DNA mixture deconvolution of sexual offense samples. A 2024 validation study for forensic applications confirmed the technology’s reliability, and other work has applied it to the deconvolution of blood-blood mixtures using separated single-cell STR profiling—one of the most challenging mixture types in forensic practice. The platform’s precision comes at a cost, however: throughput is limited by the cartridge capacity, and the expense of the system places it beyond many routine laboratories. Newer microfluidic innovations, including integrated dielectrophoretic presorting with wireless electrode arrays for high-throughput selective single-cell isolation published in 2026, and forensic lab-on-a-disc devices for enhanced sperm cell purification, suggest the field is actively working to close the throughput gap.

Isolating a cell is only half the battle. Once a single cell is captured, its DNA must be amplified, and this is where the technique encounters its most stubborn technical obstacles. A single cell contains roughly six picograms of DNA, so whole genome amplification is required before STR typing. At this extreme low-template regime, two artifacts dominate: allelic drop-out, in which one allele at a locus fails to amplify and produces a false homozygous result, and allelic drop-in, in which stray DNA from the environment contaminates the amplification and introduces alleles that were never in the original cell. Drop-out rates in single-cell STR profiles can exceed thirty percent at some loci, and stutter—artifactual peaks one repeat unit shorter than the true allele—behaves differently in single cells than in bulk samples, complicating interpretation. Researchers have developed increasingly refined amplification chemistries to mitigate these problems, including abasic-site-mediated semi-linear preamplification for low-template DNA published in 2025, and recombinase polymerase amplification of forensic STR loci, which operates at constant temperature and could enable rapid point-of-care typing.

The real forensic power emerges when investigators analyze not one cell but many, and then integrate the genotype data computationally. Because each cell carries the same genome from one contributor, clustering algorithms can group single-cell profiles by their underlying genotype, and consensus reconstruction can correct for drop-out by combining information across replicates. Research from the group of Kristen Duffy and Catherine Grgicak demonstrated that single-cell data produces genotype distributions concentrated at the true genotype across all mixture complexities, and that evidentiary evaluation of single cells renders highly informative forensic comparisons across multifarious admixtures. Probabilistic genotyping software validated for single-cell STR analysis can compute likelihood ratios from clustered single-cell replicates, and studies have shown that probabilistic genotyping of single-cell replicates from complex DNA mixtures recovers higher contributor likelihood ratios than standard analysis. The approach has even been applied to first-degree relatives, where probabilistic genotyping of single-cell replicates prevents the false inclusion of non-donor relatives—a critical safeguard in cases involving family members. Y-chromosomal haplotyping of single sperm cells isolated from semen mixtures has successfully identified three perpetrators in a multi-suspect sexual assault case, and cluster analysis has been used to group partial autosomal haplotypes derived from single sperm STR profiling.

The review also highlights the comparative performance of the three isolation categories across throughput, sample adaptability, and cost. Micromanipulation and LCM offer the finest precision and work directly on stained slides without requiring single-cell suspension, making them adaptable to degraded or limited samples, but their throughput is low and operator skill is essential. FACS and IFC deliver high throughput and quantitative classification but demand intact single-cell suspensions and expensive instrumentation. DEPArray systems provide digital precision and image-based selection but are constrained by cartridge capacity and cost. The authors note that no single technique dominates across all criteria, and the choice depends on the mixture type, the cell types involved, and the resources available. For same-cell-type mixtures—such as blood from two donors or touch DNA from multiple handlers—only single-cell strategies can physically separate the contributors, because differential extraction and other conventional methods rely on cell-type differences that do not exist in these cases.

Looking forward, the Sichuan University team identifies three converging directions that could transform single-cell forensics from a specialized tool into a routine workflow. Automation and high-throughput systems, including deep neural networks for automated sperm detection on stained slides and fully integrated microfluidic sample-in-answer-out platforms, could dramatically reduce the manual labor that currently limits casework. Artificial intelligence-assisted analysis, from convolutional networks that hunt sperm on microscope slides to machine learning models that classify cell types from morphological features, is already demonstrating feasibility in published studies. And standardized interpretation frameworks—the development of validated pipelines for multi-single-cell clustering, consensus genotype reconstruction, and probabilistic evidence evaluation—will be essential for courts to accept single-cell evidence with the same confidence as conventional profiles. The authors emphasize that the forensic value of single-cell strategies is already clear: they can recover probative DNA profile information from unresolvable minor donors, deconvolve same-cell-type mixtures that defeat all other methods, and provide genotype data that concentrates at the true contributor genotype regardless of mixture complexity. As these techniques mature, the review concludes, the combination of automated isolation, AI-assisted analysis, and standardized probabilistic interpretation could finally give investigators the power to read the full genetic story hidden in even the most tangled crime scene sample.

Subject of Research: Forensic Science

Article Title: Single-cell strategies for the interpretation of complex forensic DNA mixtures: isolation techniques, genotype data integration, and prospects for application

Article References: Liu, R., Wang, Z., & Liu, J. (2026). Single-cell strategies for the interpretation of complex forensic DNA mixtures: isolation techniques, genotype data integration, and prospects for application. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04046-y

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04046-y

Keywords: forensic DNA, single-cell analysis, DNA mixtures, STR profiling, laser capture microdissection, FACS, DEPArray, probabilistic genotyping, forensic science, legal medicine, Single-cell, strategies

The study was prompted by a real forensic case that illustrates the problem vividly. An eight-year-old male victim reported that anal penetration had occurred, and intimate swabs were sent for forensic testing. Short Tandem Repeat analysis, the standard technique for matching DNA to individuals, revealed a mixture containing an unknown major component that matched the suspect’s profile. Yet tests for semen, saliva and blood all returned negative results. Skin contact was considered an unlikely explanation for the high amount of DNA detected, and the investigators suggested pre-ejaculate as a potential source. Without a validated method to confirm the presence of this fluid, however, the source of the DNA could not be determined, and the DNA report alone could not prove that sexual activity had occurred. The detection of pre-ejaculate, the authors note, could have substantially contributed to reconstructing the course of events.

Pre-ejaculate, colloquially known as pre-cum, is produced by the bulbourethral glands, also called Cowper’s glands, which sit below the prostate within the male pelvic floor. The fluid is released during sexual arousal and serves as a natural lubricant, while also preparing the urethra for ejaculation by creating a sperm-friendly pH environment. Its composition is known to be heterogeneous, containing glucose, leukocytes, occasional epithelial cells, enzymes and glycoproteins. Importantly, the volume of secretion varies enormously between individuals, with some men producing little to none and others producing comparatively large amounts. The fluid is not only secreted before ejaculation but also during the ejaculatory phase itself, which means that pre-ejaculate and semen can become mixed in a single sample, complicating any attempt to attribute findings to one fluid or the other.

One of the most contested questions in the literature concerns whether pre-ejaculate contains spermatozoa. Previous studies have reached conflicting conclusions: some have reported the presence of sperm in collected samples, while others have found none. The German team addressed this uncertainty directly by screening every sample microscopically before analysis. Ninety-four male donors aged 20 to 59 collected samples at home using Copan FLOQSwabs, which were transported in thermal envelopes and frozen at minus 20 degrees Celsius. Using the Sperm HY-LITER kit, a human-specific monoclonal antibody-based fluorescence staining method that visualises sperm heads, the researchers examined each sample under a Zeiss Axioscope 5 fluorescence microscope. Spermatozoa were detected in 35 of the 94 samples, which were excluded from further analysis, even when only a single sperm cell was observed. The remaining 58 samples, genuinely sperm-free, formed the basis of the study.

The exclusion of nearly half the samples is itself revealing. The authors attribute the presence of sperm in so many collected specimens to contamination, most likely residual semen left in the urethra from a prior ejaculation that was washed out by the pre-ejaculate. This finding is consistent with earlier studies that reported divergent results on sperm content, and it underscores the practical difficulties of collecting pre-ejaculate without admixture. The researchers also acknowledge a residual limitation: ejaculate from azoospermic donors, who produce no detectable sperm, could theoretically have been misclassified as pre-ejaculate. This risk was reduced, though not eliminated, by recruiting donors of reproductive age and providing written instructions to collect the fluid early enough to avoid mixing with ejaculate.

With the sperm-free samples secured, the team tested how three standard forensic assays for seminal fluid reacted to pre-ejaculate, and the results were strikingly inconsistent. The RSID-Semen test, which detects semenogelin, a protein specific to seminal fluid, returned negative in all 58 samples. The Seratec PSA-Semiquant test, which detects prostate-specific antigen, was positive in 84.5 percent of samples. The Phosphatesmo KM test for acid phosphatase produced a substantial proportion of ambiguous results, with 31.0 percent of samples that could not be clearly classified; of the remainder, 29.3 percent were positive and 39.7 percent negative. The pattern suggests that low quantities of PSA and acid phosphatase may be present in pre-ejaculate, producing positive results in some samples but not others, while semenogelin, being specific to seminal fluid, is absent altogether.

These divergent test results carry serious implications for forensic practice. Because PSA and acid phosphatase assays are commonly used as presumptive tests for semen, a positive result on such a test could in principle originate from pre-ejaculate even in the complete absence of semen or seminal fluid. Conversely, a negative result, for example on a semenogelin assay, might lead investigators to exclude a sample from further DNA analysis, with the risk of missing crucial case information. The authors emphasise that this inconsistency reflects the poorly understood molecular composition of pre-ejaculate and complicates forensic interpretation in casework. Their findings align with a 2021 review by Kelly and colleagues, which first highlighted the forensic relevance of pre-ejaculate, and with prior reports that semenogelin assays yield negative results for pre-ejaculate while PSA and acid phosphatase may be present.

The DNA analysis delivered the study’s headline finding. Yields reached up to 436 nanograms, an amount far exceeding what is typically needed for genetic profiling. From 49 of the 58 samples, full STR profiles could be generated; these samples contained a mean total DNA amount of 23.616 nanograms and a median of 2.768 nanograms. Two further samples produced partial profiles, with ten fully typed STR markers and possible allelic dropouts in the remaining six systems, from DNA quantities of just 0.068 and 0.044 nanograms; despite the dropouts, both profiles would meet the criteria for submission to the national DNA database. No profile could be generated from seven samples, which had a mean DNA yield of only 0.027 nanograms. The DNA quantities observed in the study would comfortably explain the trace amounts found in the rape case that inspired the investigation, where stains in the anal canal and perianal area contained 1.272 and 6.712 nanograms respectively.

The authors are candid about the limitations of their methodology. Because donors collected samples unsupervised at home, neither the volume of fluid nor the swab handling could be standardised, and this variability likely contributed to the wide spread in DNA concentrations. A single swab was used across all analyses to rule out sperm contamination as far as possible, and DNA was extracted from the sample pad of the immunochromatographic test cassette rather than directly from the swabs, meaning only a fraction of the available material was utilised. Direct smearing of swabs onto microscope slides and filter papers, done to minimise sample loss, raises the possibility that insufficient transfer in individual samples produced false-negative results. Positive semen and negative water controls were run with each batch to monitor detection reliability, but they cannot confirm adequate material transfer in every sample.

Perhaps the deepest open question concerns where the DNA in pre-ejaculate actually comes from. Microscopic examination found isolated cells or cell-like structures in 23 of the sperm-free samples, while in the remaining 35 the findings were inconclusive. Some samples showed no detectable cells at all despite containing enough DNA for full STR typing, leaving the cellular origin of the genetic material unresolved. It remains unclear whether the DNA derives from urethral epithelial cells or from cell-free DNA, and the cellular composition of the fluid appears highly variable and poorly characterised. No validated method currently exists for the specific detection of pre-ejaculate as a distinct body fluid. The authors argue that further research is essential to characterise it reliably, both to confirm its presence at crime scenes and to differentiate it from semen. As they conclude, pre-ejaculate appears to be a key DNA source in sexual offences, and its current invisibility to routine forensic testing means that evidence central to reconstructing events may be going unnoticed.

Subject of Research: Forensic characterization of pre-ejaculate as a DNA source in sexual assault investigations

Article Title: Pre-ejaculate – an overlooked body fluid with high amounts of DNA

Article References: Lienesch, M., Sibbing, U., Schürenkamp, M., Vennemann, M., & Bauer, H. (2026). Pre-ejaculate – an overlooked body fluid with high amounts of DNA. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04003-9

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04003-9

Keywords: pre-ejaculate, forensic science, DNA, STR profiling, bulbourethral glands, semen detection, sexual assault, body fluid identification, prostate-specific antigen, acid phosphatase, semenogelin, International Journal of Legal Medicine

The core problem the researchers confronted is structural to DVI work itself. Identification by DNA typically relies on comparing post-mortem profiles recovered from remains against ante-mortem references: DNA from a toothbrush, a razor, a hairbrush, or a personal item reliably handled by the missing person. That approach collapses when a catastrophe kills whole families at once, because there is no surviving household from which to gather personal effects, and because direct relatives who would normally donate reference samples may themselves be among the victims. The October 7 massacre produced precisely this scenario across multiple communities, leaving investigators with fragmented, sometimes burned or commingled remains and a shortage of the reference material on which standard kinship matching depends. The solution proposed in the study was to mine medical archives, where every biopsy, Pap smear, surgical specimen, and diagnostic swab represents a documented, dated, and individually attributable sample of a specific patient’s DNA.

The researchers call this strategy a self-direct-reference antemortem DNA database, a term that captures its key advantage: the archived specimen is not a proxy handled by the victim, such as a toothbrush that could carry someone else’s DNA, but the victim’s own biological material collected under clinical conditions and linked to a verified identity through medical records. That distinction matters enormously in forensic practice, where misattribution of a reference sample can derail an entire identification. A paraffin block from a 2015 surgery or a cytology slide from a routine screening test carries an unbroken chain of custody through the pathology laboratory, and the DNA within it belongs, with near certainty, to the named patient. In effect, decades of routine diagnostic medicine had unknowingly been building a national ante-mortem DNA repository, waiting for a method to unlock it.

Unlocking it, however, is far from trivial, and this is where the study makes its most valuable technical contribution. Formalin fixation, the standard preservative for surgical pathology specimens, cross-links proteins and fragments DNA into short pieces, often just a few dozen to a few hundred base pairs long. Paraffin embedding adds further chemical and thermal stress over years of storage. Forensic short tandem repeat (STR) profiling, the workhorse of human identification, normally prefers intact DNA and amplifies loci that can span several hundred base pairs, so degraded archival DNA poses a real risk of allele dropout, locus amplification failure, and partial profiles. The team therefore designed a controlled optimization experiment, treating the archived specimens not as a last resort but as a material class with its own processing requirements, to be characterized systematically rather than improvised case by case.

The experimental design was straightforward but rigorous. The 151 specimens fell into three categories: 131 histological samples in the form of FFPE tissue blocks and cytology slides, 8 diagnostic swabs, and 12 blood or serum samples, all collected between 2003 and 2023. The investigators varied four parameters and measured their effect on profiling success: the tissue source of the specimen, the DNA extraction method applied, the incubation protocol used during extraction, and the age of the sample. Extracted DNA was amplified with the Investigator 24plex STR kit, and success was quantified as the number of informative autosomal STR loci recovered, with a maximum of 21 usable loci defining a fully informative profile. Descriptive statistics and non-parametric inferential tests were then applied to determine whether differences in outcomes across sample types and methods were statistically significant, which they were, confirming that processing choices genuinely matter rather than being matters of laboratory preference.

The headline result is a range of success rates spanning 67 to 100 percent of mean locus recovery, depending on tissue type and processing optimization. In practical terms, even the worst-performing specimen categories yielded profiles informative enough to contribute to identification, while the best categories performed as reliably as fresh reference material. Blood and serum samples, being less chemically assaulted than formalin-fixed tissue, sat at the favorable end of the range, as did certain tissue types within the FFPE group. The finding that sample age alone did not doom a specimen is particularly striking: blocks two decades old could still yield usable profiles when the right extraction chemistry and incubation conditions were applied. For DVI planners, this transforms the mental model of a pathology archive from a static library of diagnostic slides into a dynamic genetic resource whose yield can be predicted and maximized.

The optimization variables identified by the study carry direct operational significance. Extraction method selection determines how efficiently cross-linked, fragmented DNA is released from fixed tissue, and the literature on FFPE-derived DNA for next-generation sequencing has long shown that different extraction chemistries produce markedly different yields and fragment length distributions. The study extends that insight into the forensic STR context, where the goal is not sequencing read depth but the recovery of a sufficient number of complete, correctly sized STR amplicons. Incubation protocols, including the temperature and duration of the digestion step, similarly influence whether the fragile archival DNA is liberated intact or further sheared. By testing these variables across a real, diverse specimen collection rather than a small proof-of-concept set, the researchers produced guidance that a forensic laboratory can adopt directly, choosing the optimal workflow for each specimen type before committing irreplaceable archive material.

Beyond the immediate Israeli context, the study’s implications reach into global DVI preparedness. International guidelines, including INTERPOL’s DVI framework, emphasize ante-mortem data collection as the bottleneck of every mass fatality response, and historical operations from the Brussels Airport attack to the decades-long Korean War Identification Project illustrate how reference scarcity prolongs identifications and deepens families’ anguish. The Israeli experience adds a new layer to that body of knowledge: national health systems worldwide hold enormous, already-identified biological archives, and the study demonstrates that these archives can be converted into ante-mortem DNA references with predictable, optimizable success rates. The authors frame their findings as actionable guidance for DVI preparedness, and the phrase is apt, because the practical lesson is that countries need not wait for a catastrophe to begin cataloging, validating, and integrating their medical specimen repositories into forensic contingency planning.

There are also important scientific and ethical dimensions that the study implicitly raises. Forensic genetics in Israel operates within a legal and cultural landscape in which religious considerations, including Jewish law’s sensitivities around the treatment of human remains and autopsies, shape identification practice, making DNA-based methods that minimize invasive procedures especially valuable. The use of archived clinical specimens for identification purposes sits at the intersection of medical confidentiality, data protection, and forensic necessity, and the involvement of hospital pathology institutes alongside police forensic scientists in this study reflects the kind of institutional partnership such an approach requires. The authors report no competing interests and no external funding, and the work emerged from operational necessity rather than a pre-planned research program, which lends it the credibility of methods forged under real casework pressure.

What makes this research resonate beyond forensic circles is the way it reframes ordinary medical infrastructure as a form of civil resilience. Every pathology laboratory in the world quietly preserves a record of the people it has served, in the form of tissue blocks and slides that are retained for years or decades for clinical and legal reasons. The October 7 massacre forced Israeli scientists to recognize that this record could serve the dead and their surviving relatives when every other avenue of identification had been exhausted. The study’s systematic demonstration that 67 to 100 percent of informative STR loci can be recovered from such material, given the right extraction and amplification choices, converts a desperate improvisation into a reproducible protocol. For the families of the victims, the science delivered something no other method could: certainty about the fate of loved ones. For the global forensic community, it delivers a tested blueprint for the next inevitable mass disaster, one that begins not in the morgue but in the quiet shelves of the hospital archive.

Subject of Research: Use of archived medical specimens as ante-mortem DNA references for disaster victim identification

Article Title: Archived medical specimens as antemortem DNA references for disaster victim identification, optimization study following the October 7 massacre

Article References: Ido, A., Avrahami, K., Feinberg, T., Itzhaki-Alfia, A., & Herman, Y. (2026). Archived medical specimens as antemortem DNA references for disaster victim identification, optimization study following the October 7 massacre. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04028-0

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04028-0

Keywords: disaster victim identification, ante-mortem DNA, FFPE specimens, STR profiling, forensic genetics, mass casualty, October 7 attack, pathology archives, DNA extraction, International Journal of Legal Medicine, Israel Police, DVI preparedness

The research team, led by Maryam Sharafi Farzad and colleagues at the University of Copenhagen, set out to validate the Precision ID mtDNA Whole Genome Panel from Thermo Fisher Scientific specifically for telogen hair analysis and to implement it in routine forensic casework. Mitochondrial DNA offers a crucial advantage in this context: cells contain many more copies of mitochondrial DNA than nuclear DNA, and the molecule is far more resistant to degradation. Although mtDNA is maternally inherited and therefore lacks the discriminatory power to identify a single individual, it remains highly valuable for maternal lineage analysis, missing-person investigations, disaster victim identification, and cases where only degraded biological material is available. Traditionally, mtDNA typing relied on Sanger sequencing of the control region alone, a labor-intensive and costly approach with limited discriminatory power. Massively parallel sequencing technologies such as the Precision ID panel now allow entire mitochondrial genomes to be sequenced quickly and affordably, dramatically increasing both sensitivity and information content.

To establish the sensitivity of the workflow, the researchers prepared dilution series from NIST Standard Reference Material DNA and six reference samples, spanning an extraordinary range from 3 to 3,600 mitochondrial DNA copies per microliter. The results were striking. Complete mitochondrial genome sequences were consistently recovered in 99 percent of samples across the dilution series at DNA input levels as low as 47 mtDNA copies, demonstrating remarkable robustness under low-template conditions. Full profiles were obtained in half of the samples containing only 23 copies, and even some samples at 12 copies produced partial results. Statistical modeling using log-log linear regression revealed that library yield scaled nearly proportionally with mtDNA input in the NIST series, with a doubling of input DNA producing an approximately 2.16-fold increase in library output. Read depth increased linearly up to roughly 560 to 1,235 copies per reaction before plateauing due to saturation, underscoring the importance of accurate library quantification and normalization.

The heart of the study involved 100 volunteers who each provided 20 shed hairs collected from their own clothing, with 98 of them also contributing buccal swab samples for comparison. Microscopic examination identified the club-shaped roots characteristic of telogen hairs, and one hair per donor was selected for analysis. Quantification revealed that 98 of the 100 hair extracts met or exceeded the manufacturer-recommended input of 3,000 mtDNA copies, and both small and large mtDNA quantification targets were detected in every single sample. In contrast, 25 hairs contained no detectable nuclear DNA at all, and most of the remainder showed concentrations below 6.8 picograms per microliter with extensive degradation. The researchers also found that reducing the post-extraction volume from 50 to 30 microliters significantly increased both mtDNA copy number and sequencing read depth, a simple procedural change that boosted sensitivity without introducing contamination. Notably, donor variables such as age, gender, hair dye use, and washing habits showed no statistically significant association with mtDNA quantity or quality.

Comparing the mitochondrial genomes sequenced from 91 paired hair and buccal samples revealed fascinating subtleties of mitochondrial biology. Initial sequence concordance between hairs and their corresponding buccal references was 93.4 percent. However, when the team applied the interpretation guidelines of the International Society for Forensic Genetics and excluded low-confidence discrepancies associated with high strand bias, heteroplasmic variants, and sequencing artifacts, concordance rose to a perfect 100 percent. This finding is critically important for forensic practice: apparent mismatches between a hair and a reference sample frequently reflect technical limitations and tissue-specific heteroplasmy rather than true genetic differences. Heteroplasmy, the coexistence of multiple mitochondrial variants within an individual, arises from bottleneck effects and drift during tissue development, and previous research has shown that it can drift notably in hair. According to ISFG guidelines, a single mismatch or heteroplasmic difference should never be interpreted as evidence of exclusion, and this study provides empirical weight for that principle in the context of whole mitochondrial genome sequencing.

Reproducibility testing further strengthened the case for implementation. The researchers amplified and sequenced duplicate libraries from 43 telogen hair samples and 46 buccal samples, finding over 99 percent concordance of the software-classified true variants between replicates. The handful of discrepancies involved shifts between point and length heteroplasmy classifications, insertion-length differences at homopolymeric C-tracts, and low-frequency artifacts at known hotspots, none of which affected haplotype interpretation. Haplogroup assignments remained identical across all replicates and dilution levels, confirming that reduced template input did not compromise phylogenetic classification. The data analysis itself was also highly repeatable, with two independent runs of the Converge analysis software producing identical results across every measured parameter, from variant frequencies and read depths to strand bias metrics and variant state classifications.

Contamination control, a perennial concern in low-copy-number DNA work, was rigorously assessed. Of 16 negative controls processed during the study, none produced a complete mitochondrial DNA sequence. Six controls showed low-level mtDNA signal consisting of only two to eight variants, predominantly common polymorphisms, and none of these partial profiles corresponded to any of the analyzed samples, the NIST control, or laboratory personnel. Several variants in the controls were traced to primer binding regions, indicating primer variants rather than true biological signal. All work was conducted in a dedicated laboratory following ISFG and SWGDAM guidelines under the ISO 17025 validation framework, and every extraction, quantification, and sequencing batch included negative controls, providing a template for laboratories considering adoption of the method.

Perhaps most compelling for investigators is the performance of the validated workflow on real evidence. The team sequenced 11 archived DNA extracts from hairs collected in 2010 from concluded criminal cases, samples that had previously been deemed unsuitable for STR profiling because they contained no detectable or less than 7 picograms per microliter of nuclear DNA. Remarkably, these aged forensic samples yielded complete mitochondrial genome sequences with an average read depth of 1,037-fold, an exceptionally high coverage figure. Across the three fully reported casework samples, 102 variants were identified, 98 of which were confirmed as true variants with high confidence scores, and no nuclear mitochondrial DNA segments, or NUMTs, were detected to confound the analysis. The success demonstrates that even DNA extracts stored for over a decade can return informative whole mitochondrial genomes, offering hope for cold case reviews.

The study is not without caveats that laboratories must respect. A few amplicons, particularly those covering mitochondrial regions 8622 to 8796, 1317 to 1491, and 1948 to 2111, consistently underperformed across sample types, mirroring poor performance reported in earlier evaluations of the panel. Length heteroplasmy artifacts at homopolymeric stretches such as positions 309 and 11038 appeared with variant strand bias exceeding 0.7, requiring careful filtering. At very low template levels, below roughly 47 copies, stochastic effects increased the frequency of unlikely and unclear variant calls. The authors emphasize that reliable results from low-copy samples demand increased read allocation, replicate sequencing, manufacturer-recommended run thresholds, and stringent filtering of negative controls and NUMTs. The laboratory will continue using an input of 3,000 mtDNA copies for casework despite evidence that lower inputs can suffice, retaining a conservative margin for evidentiary work.

Taken together, the findings position whole mitochondrial genome sequencing of telogen hairs as a validated, sensitive, and contamination-controlled method ready for routine forensic implementation. With more than 85 percent of hair evidence in some laboratories currently unanalyzable by STR profiling, the ability to recover complete mitochondrial genomes from shed hairs with high read depth and near-perfect concordance when properly interpreted represents a meaningful expansion of the forensic toolkit. As massively parallel sequencing continues its migration from research laboratories into accredited casework units, hairs that once sat silently in evidence storage may soon speak, narrowing gaps in investigations, strengthening maternal lineage identifications, and giving cold cases a second chance at resolution.

Subject of Research: Validation of whole mitochondrial genome sequencing of shed telogen hairs for forensic casework

Article Title: Precision ID mtDNA Whole Genome Panel and sequencing of telogen hairs – perspectives for validation and implementation in casework

Article References: Sharafi Farzad, M., Claessens, F., Petersen, C. B., Pereira, V., Morling, N., & Mogensen, H. S. (2026). Precision ID mtDNA Whole Genome Panel and sequencing of telogen hairs – perspectives for validation and implementation in casework. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-03992-x

Image Credits: AI Generated

DOI: 10.1007/s00414-026-03992-x

Keywords: mitochondrial DNA, telogen hairs, massively parallel sequencing, Precision ID mtDNA Whole Genome Panel, forensic casework, mtDNA heteroplasmy, low-template DNA, STR profiling, profile concordance, contamination control, ISFG guidelines, hair shaft evidence