Error rates in forensic DNA analysis: Definition, numbers, impact and communication

Hungarian legislation regarding implementing a forensic DNA elimination database

The inception of forensic DNA elimination database represents a pivotal advancement in forensic science, aiming to streamline the process of distinguishing between DNA found at crime scenes and that of individuals involved in the investigation process, such as law enforcement personnel and forensic lab staff. In subsequent phases, once familiarity with the database is achieved by its administrators and other stakeholders, and they have accrued sufficient experience, the possibility of expanding the database to encompass first responders-including firefighters, paramedics, emergency medical technicians, and other emergency services personnel-can be contemplated. Key challenges in managing these databases encompass the grounds for collecting samples, ensuring the integrity of both samples and profiles, along with the duration of retention, access to the database, and the protocols to follow when a match is found in the database. This paper outlines the conceptual and detailed legislative framework in Hungary, where the forensic DNA elimination database was introduced in 2022.

Understanding 'error' in the forensic sciences: A primer

This paper distils seven key lessons about 'error' from a collaborative webinar series between practitioners at Victoria Police Forensic Services Department and academics. It aims to provide the common understanding of error necessary to foster interdisciplinary dialogue, collaboration and research. The lessons underscore the inevitability, complexity and subjectivity of error, as well as opportunities for learning and growth. Ultimately, we argue that error can be a potent tool for continuous improvement and accountability, enhancing the reliability of forensic sciences and public trust. It is hoped the shared understanding provided by this paper will support future initiatives and funding for collaborative developments in this vital domain.

Machine learning applications in forensic DNA profiling: A critical review

Machine learning (ML) is a range of powerful computational algorithms capable of generating predictive models via intelligent autonomous analysis of relatively large and often unstructured data. ML has become an integral part of our daily lives with a plethora of applications, including web, business, automotive industry, clinical diagnostics, scientific research, and more recently, forensic science. In the field of forensic DNA, the manual analysis of complex data can be challenging, time-consuming, and error-prone. The integration of novel ML-based methods may aid in streamlining this process while maintaining the high accuracy and reproducibility required for forensic tools. Due to the relative novelty of such applications, the forensic community is largely unaware of ML capabilities and limitations. Furthermore, computer science and ML professionals are often unfamiliar with the forensic science field and its specific requirements. This manuscript offers a brief introduction to the capabilities of machine learning methods and their applications in the context of forensic DNA analysis and offers a critical review of the current literature in this rapidly developing field.

Nucleic Acids Persistence-Benefits and Limitations in Forensic Genetics

The analysis of genetic material may be the only way to identify an unknown person or solve a criminal case. Often, the conditions in which the genetic material was found determine the choice of the analytical method. Hence, it is extremely important to understand the influence of various factors, both external and internal, on genetic material. The review presents information on DNA and RNA persistence, depending on the chemical and physical factors affecting the genetic material integrity. One of the factors taken into account is the time elapsing to genetic material recovery. Temperature can both preserve the genetic material or lead to its rapid degradation. Radiation, aquatic environments, and various types of chemical and physical factors also affect the genetic material quality. The substances used during the forensic process, i.e., for biological trace visualization or maceration, are also discussed. Proper analysis of genetic material degradation can help determine the post-mortem interval (PMI) or time since deposition (TsD), which may play a key role in criminal cases.

Reliability of the P3 component in a 3-stimulus concealed information test with known and unknown stimuli

The parietal P3 amplitude of the event-related potential (ERP) has been highlighted to signal stimulus salience in concealed information tests (CITs) with known and unknown stimuli. To extend previous validity investigations in deception research, the reliability of the early parietal P3 amplitude in a 3-stimulus CIT including known and unknown stimuli has been investigated in a sample of N = 68 participants. Variations of Cronbach's Alpha and split-half reliability (odd-even, 1st vs. 2nd half) of the early parietal P3 amplitude were considered for ERP quantification method (peak-to-peak, mean, baseline-to-peak), epoch selection strategies (chronological vs. random) and number of epochs (10-40) in three stimulus types (probe, target, irrelevant). Excellent reliability coefficients have been summarized for number of epochs, P3 quantifications, and epoch selection strategies. Moreover, the best-practice recommendations highlight mandatory combinations of epoch selection strategy, number of epochs and P3 quantifications to ensure robust and excellent reliabilities of the early parietal P3 amplitude in a 3-stimulus CIT with known (probe, target) and unknown (irrelevant) stimuli. The robustness of mandatory excellent reliability coefficients for the early parietal P3 has been discussed for two data tracks in single-case analyses.

DNA accumulation and transfer within an operational forensic exhibit storeroom

The increased sensitivity of current DNA profiling technologies allows the detection of trace amounts of DNA. With these advancements, there is an increased probability of detecting trace levels of DNA from contamination. Studies which investigate the accumulation and transfer of DNA within forensic laboratories provide insight into the possible mechanisms which may result in the contamination of exhibits. To gain a greater understanding of the level of DNA transfer between exhibit packaging and forensic workspaces, the accumulation of DNA within an operational forensic exhibit storeroom was investigated. Samples were collected from previously cleaned forensic exhibit storeroom shelves at various time points over a 14-week period. To determine the source of accumulating DNA, profiles generated from shelf samples were compared to the laboratory staff elimination database and the profiles generated from exhibits stored on each of the shelves sampled over the course of the study. Additionally, all samples were compared using STRmix™ mixture-to-mixture profile analysis, to identify the presence of common non-staff DNA donors and DNA from exhibits stored on the shelves sampled. As sampling time intervals increased, there was a significant increase in DNA quantity (ng) and number of profile contributors. The shelf height was also observed to influence the number of profile contributors, with higher numbers of contributors being found on lower shelves. DNA profiles generated from the shelf samples were matched to DNA from forensic staff members who enter the storeroom and police employees, who do not enter the storeroom. There were three instances where a common DNA profile contributor was identified between a shelf sample and the profile generated from an exhibit.This study provides insight into whether current exhibit storage procedures are still adequate given the highly sensitive DNA profiling systems currently used.

The potential for investigator-mediated contamination to occur during routine search activities

The sensitivity and discrimination power of modern DNA profiling systems means that very small amounts of DNA from an individual can be detected on an item leading to large inclusionary statistics for that person. The sensitivity of these systems has significant benefits in the investigation of crime but also can be highly sensitive to contamination of exhibits or crime scenes. It becomes critical to distinguish between deposition during commission of a crime or deposition via some other method unrelated to the crime. This study investigates methodologies used in crime scene examination and the potential for them to cause non-crime-related transfer of DNA. Factors assessed include the source of DNA, the handling time, the amount of movement during contact, and the substrate type. The amount of movement and the number of transfer steps are the most critical in determining whether, and how much, DNA is transferred. This study provides information for crime scene examiners and also scientists assessing transfer scenarios.

A Logical Framework for Forensic DNA Interpretation

The forensic community has devoted much effort over the last decades to the development of a logical framework for forensic interpretation, which is essential for the safe administration of justice. We review the research and guidelines that have been published and provide examples of how to implement them in casework. After a discussion on uncertainty in the criminal trial and the roles that the DNA scientist may take, we present the principles of interpretation for evaluative reporting. We show how their application helps to avoid a common fallacy and present strategies that DNA scientists can apply so that they do not transpose the conditional. We then discuss the hierarchy of propositions and explain why it is considered a fundamental concept for the evaluation of biological results and the differences between assessing results given propositions that are at the source level or the activity level. We show the importance of pre-assessment, especially when the questions relate to the alleged activities, and when transfer and persistence need to be considered by the scientists to guide the court. We conclude with a discussion on statement writing and testimony. This provides guidance on how DNA scientists can report in a balanced, transparent, and logical way.

GITAD 2020: quality assurance test through 20 years of experience

GITAD (Grupo Iberoamericano de Trabajo en Análisis de DNA) was founded in 1998 as the first operational group of AICEF (Academia Iberoamericana de Criminalística y Estudios Forenses), formally created in 1999. The mission and the vision of GITAD are to promote the development of forensic genetics in Ibero-American countries and to achieve the maximum level of innovation and quality in each country, and with that aim, a proficiency test was developed. Since 1999, the member laboratories receive four reference samples with the objective of obtaining the genetic profile with their routine protocols, a theoretical exercise since 2003, and since 2007, it was incorporated a forensic sample, which changes every year. The consensus results and the different discrepancies are discussed in an annual meeting. This article illustrates the evolution of the proficiency test through 20 years from different points of view: the increase of participant laboratories, the evolution of the different DNA typing techniques reported by the Ibero-American participant laboratories, the challenges that the proficiency test have met, and future perspectives for a continuous improvement of the proficiency test, especially regarding its accreditation under ISO 17043.

Comparison between various DNA sterilization procedures applied in forensic analysis

Background

The advanced sensitive STR kits applied in forensic DNA typing techniques can cause challenging issues when evidence samples are contaminated with minute quantities of DNA from another source such as forensic analysts or crime scene examiners.

Results

In this study, laboratory air and surfaces, gloves, tools, and equipment were evaluated as potential sources of contaminating DNA. Different sterilization methods were tested for their ability to efficiently eliminate DNA in a sample. Inactivation methods included 10% bleach, ethanol, UV light, and DNA-ExitusPlus IF. Exposure to the different inactivation protocols for varying periods of time was performed in two lab settings: low template DNA and DNA database labs. Surfaces were swabbed and any adhering DNA was quantified using HID real-time PCR. Results were detected using HID Real-Time PCR Analysis Software v1.2 and GeneMapper ID-X Software v1.4.

Conclusions

It was concluded that most of the DNA decontamination methods are not suitable for highly sensitive and precision STR kits such as GlobalFiler PCR Amplification Kit. The most suitable tested method was using DNA-ExitusPlus IF with the incubation time increased from 10 to 15 min.

Evaluation of Different Cleaning Strategies for Removal of Contaminating DNA Molecules

Decontamination strategies and their efficiencies are crucial when performing routine forensic analysis, and many factors influence the choice of agent to use. In this study, the effects of ten different cleaning strategies were evaluated to compare their ability to remove contaminating DNA molecules. Cell-free DNA or blood was deposited on three surfaces (plastic, metal, and wood) and decontaminated with various treatments. The quantities of recovered DNA, obtained by swabbing the surfaces after cleaning using the different strategies, was analyzed by real-time PCR. Large differences in the DNA removal efficiencies were observed between different cleaning strategies, as well as between different surfaces. The most efficient cleaning strategies for cell-free DNA were the different sodium hypochlorite solutions and Trigene^®, for which a maximum of 0.3% DNA was recovered on all three surfaces. For blood, a maximum of 0.8% of the deposited DNA was recovered after using Virkon^® for decontamination. The recoveries after using these cleaning strategies correspond to DNA from only a few cells, out of 60 ng of cell-free DNA or thousands of deposited blood cells.

What's on the bag? The DNA composition of evidence bags pre- and post-exhibit examination

Current forensic DNA profiling kits and techniques enable the detection of trace amounts of DNA. With advancements in kit sensitivity, there is an increased probability of detecting DNA from contamination. Research into DNA transfer within operational forensic laboratories provides insight into the possible mechanisms that may lead to exhibit contamination. To gain a greater understanding of the potential for evidence bags to act as DNA transfer vectors, the level of DNA accumulating on the exterior of evidence bags during the exhibit examination process was investigated. The exterior of 60 evidence bags were tapelifted before and after the examination of the exhibit inside of the bag resulting in 120 DNA profiles. These DNA profiles were compared to DNA profiles of staff working within the building and samples taken from the exhibit inside the bag. Common DNA profile contributors from each sample were also identified through STRmix™ mixture to mixture analysis. The average DNA quantity and number of profile contributors was higher in samples taken from the bag before exhibit examination than after examination. Fifty six percent of all samples taken identified a match between DNA recovered from the evidence bag and at least one staff member. On 11 bags, a common contributor was identified between the exhibit in the bag and the exhibit package post-examination. In one instance a DNA profile, matching that of a donor, on the exhibit bag before examination was also detected on a sample taken from the exhibit, raising the possibility of outer bag-to-exhibit DNA contamination. This study demonstrates that operational forensic laboratories must consider exhibit packages as a potential source of DNA contamination and evaluate their exhibit handling and storage procedures accordingly.

Shifting forensic science focus from means to purpose: A path forward for the discipline?

Forensic science is facing a persistent crisis that is often addressed by organizational responses, with a strong focus on the improvement and standardisation of means and processes. However, organisations and processes are highly dependent on the political, economical and legal structures in which they operate. This may explain why most proposed solutions had difficulties in addressing the crisis up to now, as they could hardly be applied transversally to all forensic science models. Moreover, new tools and technologies are continuously developed by a quasi-infinite number of different scientific disciplines, thus leading to further diversity and fragmentation of forensic science. In this paper, it is proposed to shift the focus from means to purpose and consider forensic science current challenges in terms of discipline, before addressing organisations' specific issues. As a distinct discipline, forensic science can refocus research and development on shared principles and purposes, such as reconstructing, monitoring, and preventing crime and security issues. This focus change will facilitate a better understanding of the trace as the object of study of forensic science and eventually lead to a more impactful and long-lasting effect. This approach will also foster the development of a forensic science culture (instead of a primarily technological culture) unified by purpose rather than means through more relevant education and research.

Applying posterior probability informed thresholds to traditional cranial trait sex estimation methods

Sex estimation methods using traditional cranial nonmetric traits utilize predictive models to produce a final sex estimation, using the resulting model's score to classify the individual. When sex estimations are assigned from discriminant scoring alone, statistical confidence in the resultant estimate is not always assessed or reported. Although some forensic anthropologists may qualitatively report their confidence in the assessment (e.g., "probable male"), these statements are subjective, not standardized, and not necessarily based on statistical results in a uniform way. The goals of this study were to evaluate how posterior probability-informed thresholds (PPITs) impacted accuracy rates, assess the balance between sample inclusion and accuracy for the proposed PPIT approach, and make recommendations for the use and interpretation of specific thresholds in casework. Using a sample of U.S. Black and White females and males (n = 292), we examined how PPITs can standardize the decision-making process of inferring sex for two methods using nonmetric cranial traits. We found that using PPITs of at least 0.85 increased accuracy (over 92% for some PPITs) yet remained highly inclusive of the sample. PPITs < 0.75 did not produce classification accuracy rates significantly higher than chance, and when using these cranial trait sex estimation methods, cases with posterior probabilities (PPs) <0.75 should be reported as "indeterminate." The 0.75-0.84 PPIT interval had an accuracy rate of 76%, which was both statistically significantly different from chance as well as from the higher (>0.85) groups, suggesting that although sex estimation at this level may be acceptable, the results hold lower confidence.

A Review of Probabilistic Genotyping Systems: EuroForMix, DNAStatistX and STRmix™

Probabilistic genotyping has become widespread. EuroForMix and DNAStatistX are both based upon maximum likelihood estimation using a γ model, whereas STRmix™ is a Bayesian approach that specifies prior distributions on the unknown model parameters. A general overview is provided of the historical development of probabilistic genotyping. Some general principles of interpretation are described, including: the application to investigative vs. evaluative reporting; detection of contamination events; inter and intra laboratory studies; numbers of contributors; proposition setting and validation of software and its performance. This is followed by details of the evolution, utility, practice and adoption of the software discussed.

Judges and forensic science education: A national survey

In criminal cases, forensic science reports and expert testimony play an increasingly important role in adjudication. More states now follow a federal reliability standard, which calls upon judges to assess the reliability and validity of scientific evidence. Little is known about how judges view their own background in forensic scientific evidence, and what types of specialized training they receive on it. In this study, we surveyed 164 judges from 39 different U.S. states, who attended past trainings at the National Judicial College. We asked these judges about their background in forensic science, their views concerning the reliability of common forensic disciplines, and their needs to better evaluate forensic science evidence. We discovered that judges held views regarding the scientific support for different forensic science disciplines that were fairly consistent with available literature; their error rate estimates were more supported by research than many estimates by laypersons, who often assume forensic methods are nearly infallible. We did not find any association between how judges rate forensic reliability and prior training. We did, however, find that training corresponded with judges' views that they should, and do in fact, take on a more active gatekeeping role regarding forensics. Regarding the tools judges need to vet forensic experts and properly evaluate forensic science evidence, they reported having very different backgrounds in relevant scientific concepts and having forensic science education needs. Judges reported needs in accessing better material concerning reliability of forensic science methods. These results support new efforts to expand scientific evidence education in the judiciary.

Reliability of the N2-component in a modified 3-stimulus concealed information test: On the importance of excellent measurement accuracy

Research on deception focused on the investigation of event-related potentials (ERP) to facilitate our knowledge on cognitive-motivational processes underlying deception. We investigated the reliability of the frontal N2 amplitude in a modified Concealed Information Test (CIT) (N = 64 participants). Variations of Cronbach's Alpha coefficients were examined for number of epochs per stimulus type, task modality and types of ERP quantification. Cronbach's Alpha coefficients of the N2 increased with the number of epochs across task modality, stimulus types and electrode positions. In a pictorial CIT, the frontal N2 indicated excellent Cronbach's Alpha coefficients (≥ 0.90) across electrode positions and quantification methods for 25 epochs per stimulus type. At least 15 epochs were necessary to achieve excellent Cronbach's Alpha coefficients (≥ 0.90) of the peak-to-peak N2 in a modified CIT across electrode positions and stimulus types. We provide best-practice advises for the necessity to assess N2 in a modified CIT with excellent reliability.

Incidents in Molecular Pathology: Frequency and Causes During Routine Testing

CONTEXT.—

Errors in laboratory medicine could compromise patient safety. Good laboratory practice includes identifying and managing nonconformities in the total test process. Varying error percentages have been described in other fields but are lacking for molecular oncology.

OBJECTIVES.—

To gain insight into incident causes and frequency in the total test process from 8 European institutes routinely performing biomarker tests in non-small cell lung cancer and colorectal cancer.

DESIGN.—

All incidents documented in 2018 were collected from all hospital services for pre-preanalytical entries before the biomarker test, as well as specific incidents for biomarker tests.

RESULTS.—

There were 5185 incidents collected, of which 4363 (84.1%) occurred in the pre-preanalytical phase (all hospital services), 2796 of 4363 (64.1%) related to missing or incorrect request form information. From the other 822 specific incidents, 166 (20.2%) were recorded in the preanalytical phase, 275 (33.5%) in the analytical phase, and 194 (23.6%) in the postanalytical phase, mainly due to incorrect report content. Only 47 of 822 (5.7%) incidents were recorded in the post-postanalytical phase, and 123 (15.0%) in the complete total test process. For 17 of 822 (2.1%) incidents the time point was unknown. Pre-preanalytical incidents were resolved sooner than incidents on the complete process (mean 6 versus 60 days). For 1215 of 5168 (23.5%) incidents with known causes a specific action was undertaken besides documenting them, not limited to accredited institutes.

CONCLUSIONS.—

There was a large variety in the number and extent of documented incidents. Correct and complete information on the request forms and final reports are highly error prone and require additional focus.

Causes behind error rates for predictive biomarker testing: the utility of sending post-EQA surveys

External quality assessment (EQA) schemes assess the performance of predictive biomarker testing in lung and colorectal cancer and have previously demonstrated variable error rates. No information is currently available on the underlying causes of incorrect EQA results in the laboratories. Participants in EQA schemes by the European Society of Pathology between 2014 and 2018 for lung and colorectal cancer were contacted to complete a survey if they had at least one analysis error or test failure in the provided cases. Of the 791 surveys that were sent, 325 were completed including data from 185 unique laboratories on 514 incorrectly analyzed or failed cases. For the digital cases and immunohistochemistry, the majority of errors were interpretation-related. For fluorescence in situ hybridization, problems with the EQA materials were reported frequently. For variant analysis, the causes were mainly methodological for lung cancer but variable for colorectal cancer. Post-analytical (clerical and interpretation) errors were more likely detected after release of the EQA results compared to pre-analytical and analytical issues. Accredited laboratories encountered fewer reagent problems and more often responded to the survey. A recent change in test methodology resulted in method-related problems. Testing more samples annually introduced personnel errors and lead to a lower performance in future schemes. Participation to quality improvement projects is important to reduce deviating test results in laboratories, as the different error causes differently affect the test performance. EQA providers could benefit from requesting root cause analyses behind errors to offer even more tailored feedback, subschemes, and cases.

How can courts take into account the uncertainty in a likelihood ratio?

As legal practitioners and courts become more aware of scientific methods and evidence evaluation, they are demanding measures of the reliability of expert opinion. In particular, there are calls for error rates to accompany opinion evidence in comparative forensic sciences. While error rates or confidence intervals can be useful for those disciplines that claim to identify the source of a trace, the call for these statistical tools has extended to sciences that present opinions in the form of a likelihood ratio. In this article we argue against presenting both a likelihood ratio and numerical measures of its uncertainty. We explain how the LR already encapsulates uncertainty. Instead we consider how sensitivity analyses can be used to guide the presentation of LRs that are informative to the court and not unfair to defendants.

The STRidER Report on Two Years of Quality Control of Autosomal STR Population Datasets

STRidER, the STRs for Identity ENFSI Reference Database, is a curated, freely publicly available online allele frequency database, quality control (QC) and software platform for autosomal Short Tandem Repeats (STRs) developed under the endorsement of the International Society for Forensic Genetics. Continuous updates comprise additional STR loci and populations in the frequency database and many further STR-related aspects. One significant innovation is the autosomal STR data QC provided prior to publication of datasets. Such scrutiny was lacking previously, leaving QC to authors, reviewers and editors, which led to an unacceptably high error rate in scientific papers. The results from scrutinizing 184 STR datasets containing >177,000 individual genotypes submitted in the first two years of STRidER QC since 2017 revealed that about two-thirds of the STR datasets were either being withdrawn by the authors after initial feedback or rejected based on a conservative error rate. Almost no error-free submissions were received, which clearly shows that centralized QC and data curation are essential to maintain the high-quality standard required in forensic genetics. While many errors had minor impact on the resulting allele frequencies, multiple error categories were commonly found within single datasets. Several datasets contained serious flaws. We discuss the factors that caused the errors to draw the attention to redundant pitfalls and thus contribute to better quality of autosomal STR datasets and allele frequency reports.

Bayesian networks and dissonant items of evidence: A case study

The assessment of different items of evidence is a challenging process in forensic science, particularly when the relevant elements support different inferential directions. In this study, a model is developed to assess the joint probative value of three different analyses related to some biological material retrieved on an object of interest in a criminal case. The study shows the ability of probabilistic graphical models, say Bayesian networks, to deal with complex situations, those that one expects to face in real cases. The results obtained by the model show the importance of a conflict measure as an indication of inconsistencies in the model itself. A contamination event alleged by the defense is also introduced in the model to explain and solve the conflict. The study aims to give an insight in the application of a probabilistic model to real criminal cases.

Perceptions and estimates of error rates in forensic science: A survey of forensic analysts

Every scientific technique features some error, and legal standards for the admissibility of scientific evidence (e.g., Daubert v. Merrill Dow Pharmaceuticals, Inc., 1993; Kumho Tire Co v. Carmichael, 1999) guide trial courts to consider known error rates. However, recent reviews of forensic science conclude that error rates for some common techniques are not well-documented or even established (e.g., NAS, 2009; PCAST, 2016). Furthermore, many forensic analysts have historically denied the presence of error in their field. Therefore, it is important to establish what forensic scientists actually know or believe about errors rates in their disciplines. We surveyed 183 practicing forensic analysts to examine what they think and estimate about error rates in their various disciplines. Results revealed that analysts perceive all types of errors to be rare, with false positive errors even more rare than false negatives. Likewise, analysts typically reported that they prefer to minimize the risk of false positives over false negatives. Most analysts could not specify where error rates for their discipline were documented or published. Their estimates of error in their fields were widely divergent - with some estimates unrealistically low.

European follow-up of incorrect biomarker results for colorectal cancer demonstrates the importance of quality improvement projects

Biomarker analysis for colorectal cancer has been shown to be reliable in Europe with 97% of samples tested by EQA participants to be correctly classified. This study focuses on errors during the annual EQA assessment. The aim was to explore the causes and actions related to the observed errors and to provide feedback and assess any improvement between 2016 and 2017. An electronic survey was sent to all laboratories with minimum one genotyping error or technical failure on ten tumor samples. A workshop was organized based on 2016 survey responses. Improvement of performance in 2017 was assessed for returning participants (n = 76), survey respondents (n = 13) and workshop participants (n = 4). Survey respondents and workshop participants improved in terms of (maximum) analysis score, successful participation, and genotyping errors compared to all returning participants. In 2016, mostly pre- and post-analytical errors (both 25%) were observed caused by unsuitability of the tumor tissue for molecular analysis. In 2017, most errors were due to analytical problems (50.0%) caused by methodological problems. The most common actions taken (n = 58) were protocol revisions (34.5%) and staff training (15.5%). In 24.1% of issues identified no action was performed. Corrective actions were linked to an improved performance, especially if performed by the pathologist. Although biomarker testing has improved over time, error occurrence at different phases stresses the need for quality improvement throughout the test process. Participation to quality improvement projects and a close collaboration with the pathologist can have a positive influence on performance.

Positive impact of DNA contamination minimization procedures taken within the laboratory

DNA contamination incidents are one of the most frequent sources of error in forensic genetics and can have serious consequences. It is therefore essential to take measures to prevent these events and to monitor the real impact of contamination minimization procedures. In this study, we review and compare the number of contamination events detected on trace samples analyzed by the Forensic Genetic Unit (FGU) of the University Center of Legal Medicine in Switzerland before and after the implementation of new contamination minimization procedures. Interestingly, the number of contamination events by laboratory staff was significantly reduced by more than 70% after the implementation of the procedures. However, no significant change was observed for contamination events by police collaborators. This difference is likely to be explained by the differential impact of procedures taken in the laboratory and on crime scene. It suggests that the reduction observed for laboratory contamination incidents is due to the new procedures taken. In conclusion, our study highlights that taking appropriate measures is efficient and can reduce the number of contamination incidents. However, it is important that such contamination minimization procedures be implemented all along the chain of analysis of a stain (i.e. from crime scene to the laboratory).

Lessons from a study of DNA contaminations from police services and forensic laboratories in Switzerland

In Switzerland, the DNA profiles of police officers collecting crime scene traces as well as forensic genetic laboratories employees are stored in the staff index of the national DNA database to detect potential contaminations. Our study aimed at making a national inventory of contaminations to better understand their origin and to make recommendations in order to decrease their occurrence. For this purpose, a retrospective questionnaire was sent to both police services and forensic genetic laboratories for each case where there was a contamination. Between 2011 and 2015, a total of 709 contaminations were detected. This represents a mean of 11.5 (9.6-13.4) contaminations per year per 1'000 profiles sent to the Swiss DNA database. Feedbacks were obtained from the police, the laboratory or both for 552/709 (78%) of the contaminations. Approximately 86% of these contaminations originated from police officers whereas only 11% were from genetic laboratories employees and 3% were associated to other sources (e.g. positive controls, stain-stain contaminations). Interestingly, a direct contact between the stain and the contaminant person occurred in only 51% of the laboratory contaminations whereas this number increased to 91% for police collaborators. The high level of indirect DNA transfer in laboratories might be explained by the presence of "DNA reservoirs" suggesting that cleaning procedures should be improved. At the police level, most contaminations originated from the person who collected the trace and likely occurred directly at the crime scene. Improving sampling practices could be beneficial to reduce these contaminations.

Results of a collaborative study on DNA identification of aged bone samples

AIM

A collaborative exercise with several institutes was organized by the Forensic DNA Service (FDNAS) and the Institute of the Legal Medicine, 2nd Faculty of Medicine, Charles University in Prague, Czech Republic, with the aim to test performance of different laboratories carrying out DNA analysis of relatively old bone samples.

METHODS

Eighteen laboratories participating in the collaborative exercise were asked to perform DNA typing of two samples of bone powder. Two bone samples provided by the National Museum and the Institute of Archaelogy in Prague, Czech Republic, came from archeological excavations and were estimated to be approximately 150 and 400 years old. The methods of genetic characterization including autosomal, gonosomal, and mitochondrial markers was selected solely at the discretion of the participating laboratory.

RESULTS

Although the participating laboratories used different extraction and amplification strategies, concordant results were obtained from the relatively intact 150 years old bone sample. Typing was more problematic with the analysis of the 400 years old bone sample due to poorer quality.

CONCLUSION

The laboratories performing identification DNA analysis of bone and teeth samples should regularly test their ability to correctly perform DNA-based identification on bone samples containing degraded DNA and potential inhibitors and demonstrate that risk of contamination is minimized.

Probabilistically determining the cellular source of DNA derived from differential extractions in sexual assault scenarios

Sexual assault cases are the type of case that often produces questions about the cellular source of DNA. In these cases multiple findings of microscopy, DNA profiling and presumptive testing need to be considered when addressing source level propositions. In this work, I consider a line of questioning that has been raised a number of times in the recent past, where in court it was disputed that low levels of sperm seen on a microscope slide were the cellular source of the male DNA profile component generated from the sperm fraction of a differential DNA extraction. I demonstrate how the cell scoring results and DNA profiling results can be considered together, in helping address this source level question through the use of Bayesian Networks.

Leading-edge forensic DNA analyses and the necessity of including crime scene investigators, police officers and technicians in a DNA elimination database

In recent years, sophisticated technology has significantly increased the sensitivity and analytical power of genetic analyses so that very little starting material may now produce viable genetic profiles. This sensitivity however, has also increased the risk of detecting unknown genetic profiles assumed to be that of the perpetrator, yet originate from extraneous sources such as from crime scene workers. These contaminants may mislead investigations, keeping criminal cases active and unresolved for long spans of time. Voluntary submission of DNA samples from crime scene workers is fairly low, therefore we have created a promotional method for our staff elimination database that has resulted in a significant increase in voluntary samples since 2011. Our database enforces privacy safeguards and allows for optional anonymity to all staff members. We also offer information sessions at various police precincts to advise crime scene workers of the importance and success of our staff elimination database. This study, a pioneer in its field, has obtained 327 voluntary submissions from crime scene workers to date, of which 46 individual profiles (14%) have been matched to 58 criminal cases. By implementing our methods and respect for individual privacy, forensic laboratories everywhere may see similar growth and success in explaining unidentified genetic profiles in stagnate criminal cases.

Familias 3 - Extensions and new functionality

In relationship testing the aim is to determine the most probable pedigree structure given genetic marker data for a set of persons. Disaster Victim Identification (DVI) based on DNA data from presumed relatives of the missing persons can be considered to be a collection of relationship problems. Forensic calculations in investigative mode address questions like "How many markers and reference persons are needed?" Such questions can be answered by simulations. Mutations, deviations from Hardy-Weinberg Equilibrium (or more generally, accounting for population substructure) and silent alleles cannot be ignored when evaluating forensic evidence in case work. With the advent of new markers, so called microvariants have become more common. Previous mutation models are no longer appropriate and a new model is proposed. This paper describes methods designed to deal with DVI problems and a new simulation model to study distribution of likelihoods. There are softwares available, addressing similar problems. However, for some problems including DVI, we are not aware of freely available validated software. The Familias software has long been widely used by forensic laboratories worldwide to compute likelihoods in relationship scenarios, though previous versions have lacked desired functionality, such as the above mentioned. The extensions as well as some other novel features have been implemented in the new version, freely available at www.familias.no. The implementation and validation are briefly mentioned leaving complete details to Supplementary sections.