Assessment of approximate likelihood ratios from continuous distributions: a case study of digital camera identification

A reported likelihood ratio for the value of evidence is very often a point estimate based on various types of reference data. When presented in court, such frequentist likelihood ratio gets a higher scientific value if it is accompanied by an error bound. This becomes particularly important when the magnitude of the likelihood ratio is modest and thus is giving less support for the forwarded proposition. Here, we investigate methods for error bound estimation for the specific case of digital camera identification. The underlying probability distributions are continuous and previously proposed models for those are used, but the derived methodology is otherwise general. Both asymptotic and resampling distributions are applied in combination with different types of point estimators. The results show that resampling is preferable for assessment based on asymptotic distributions. Further, assessment of parametric estimators is superior to evaluation of kernel estimators when background data are limited.     

DNA分型实验室管理应重视的几个问题

1985年Gill等第一次报导将DNA指纹图用于个体讽别并获得成功后，DNA分型技术在个体识别和亲子鉴定中的应用潜力开始为法医界所注目【'］．随着该项技术的日益完善，它极大地提高了生物学检材（血液，血痕，精斑，混合斑，毛发和指甲等）在法医物证学鉴定过程中的价值，并广泛应用于法医鉴定实践中．同时，法医界又面临着这样一个问题：如何对有关的DNA分型实验室进行管理监督，以保证其能更好地为司法实践服务．本文从DNA分型实验室人员设置和要求，DNA分型技术标准化以及与传统血型血清学的关系等方面并结合国外进展作如下探讨．ID…     

DNase-I纯化结合碱性裂解法提取混合斑精子DNA

目的研究脱氧核糖核酸酶I(DNase-I)纯化结合碱性裂解法提取混合斑精子DNA的方法在法医学中的应用。方法收集79份性犯罪案件混合斑检材,分别用DNase-I纯化结合碱性裂解法和差异裂解法提取精子DNA,采用STR荧光标记复合扩增体系进行16个STR基因座分型,并比较检验结果。结果应用DNase-I纯化结合碱性裂解法提取精子DNA,64例检材分型成功;应用差异裂解法提取精子DNA,57例检材分型成功;两种方法比较结果存在显著性差异(P=0.039),DNase-1纯化结合碱性裂解法提取精子DNA的STR分型成功率更高,成本低廉。结论DNase-I纯化结合碱性裂解法提取混合斑精子DNA可提高检验成功率,操作简便,快速,易于自动化,适于法医学个体识别鉴定。     

Estimating the Number of Contributors to Forensic DNA Mixtures: Does Maximum Likelihood Perform Better Than Maximum Allele Count?

Abstract: Determining the number of contributors to a forensic DNA mixture using maximum allele count is a common practice in many forensic laboratories. In this paper, we compare this method to a maximum likelihood estimator, previously proposed by Egeland et al., that we extend to the cases of multiallelic loci and population subdivision. We compared both methods’ efficiency for identifying mixtures of two to five individuals in the case of uncertainty about the population allele frequencies and partial profiles. The proportion of correctly resolved mixtures was >90% for both estimators for two‐ and three‐person mixtures, while likelihood maximization yielded success rates 2‐ to 15‐fold higher for four‐ and five‐person mixtures. Comparable results were obtained in the cases of uncertain allele frequencies and partial profiles. Our results support the use of the maximum likelihood estimator to report the number of contributors when dealing with complex DNA mixtures.     

“中国罪犯DNA数据库“模式库:13个STR位点基因在中国人群中的分布

目的:对D3S1358、vWA、FGA、D8S1179、D21S11、D18S51、D5S818、D13S317、D16S539、THO1、TPOX、CSF1PO、D7S820等13个STR位点进行多态性调查,探索其用于"罪犯DNA数据库"的可行性.方法:用多重PCR和四色荧光自动化检测技术分析13个STR位点的基因型,计算各位点等位基因的分布频率.结果:获得13个STR位点在中国南北汉族、维吾尔族、回族人群中的等位基因分布频率资料.结论:上述位点适合作为中国人群的遗传学标志,用于"中国罪犯DNA数据库"的建立.     

Value of DNA evidence in detecting crime

DNA material is now collected routinely from crime scenes for a wide range of offences and the timely processing of the DNA is seen as key to its success in investigating and detecting crime. An analysis of DNA material recovered from the volume crime offences of residential burglary, commercial burglary, and theft of motor vehicle in Northamptonshire, U.K., in 2004 has enabled the DNA to be categorized into seven sources. Further analysis using a logistical regression has revealed a number of predictors, other than timeliness, that greatly influence whether the DNA material recovered from a crime scene enables the crime to be detected. The results indicate that a number of these predictors are of statistical significance and may be just as relevant in determining whether DNA successfully detects the crime as the timeliness of the processing of the DNA material. The most significant predictor was found to be investigating officer accreditation with location, quantity, and type of DNA material at the crime scene also being relevant. Accreditation of the Crime Scene Examiner recovering the DNA material was found not to be significant. Consideration is given to where further emphasis is needed by the U.K. police service to maximize the opportunities to detect volume crime with DNA.     

DNA sequence characterization of the FGA STR locus in the free state population of South Africa

POPULATION: African (n=52), Mixed Ancestry (n=5), Caucasian (n=4) SAN (n=1).     

Knowledge on DNA Success Rates to Optimize the DNA Analysis Process: From Crime Scene to Laboratory

DNA analysis has become an essential intelligence tool in the criminal justice system for the identification of possible offenders. However, it appears that about half of the processed DNA samples contains too little DNA for analysis. This study looks at DNA success rates within 28 different categories of trace exhibits and relates the DNA concentration to the characteristics of the DNA profile. Data from 2260 analyzed crime samples show that cigarettes, bloodstains, and headwear have relatively high success rates. Cartridge cases, crowbars, and tie‐wraps are on the other end of the spectrum. These objective data can assist forensics in their selection process.The DNA success probability shows a positive relation with the DNA concentration. This finding enables the laboratory to set an evidence‐based threshold value in the DNA analysis process. For instance, 958 DNA extracts had a concentration value of 6 pg/μL or less. Only 46 of the 958 low‐level extracts provided meaningful DNA profiling data.     

磁珠法对混合斑中精子DNA批量自动提取的应用研究

目的 建立混合斑中精子DNA批量自动提取的方法.方法 对56例混合斑经第一步消化后的精子沉淀用DNA IQ试剂盒和Biomek（R）2000全自动核酸工作站自动提取纯化,3130xl型遗传分析仪分析结果.结果 56例混合斑检材均得到较好的STR分型结果.结论 DNA IQ试剂盒和Biomek（R）2000全自动核酸工作站批量自动提取纯化混合斑的方法快速简便,可应用于法庭科学实践.     

Analysis of Mitochondrial DNA from a Burned,Ninhydrin‐Treated Paper Towel

Contact‐based evidence is likely to have limited quantities of DNA and may yield mixed profiles due to preexisting or contaminating DNA. In a recent arson investigation, a paper towel was collected and used as circumstantial evidence. The paper towel was partially burned and was likely set on fire with flammable liquid. As part of the investigation, the paper towel was treated with ninhydrin to visualize fingerprint evidence. Initial DNA analysis of two swabs was negative for short tandem repeat (STR) markers and revealed a mixture of mitochondrial DNA (mtDNA). Analysis of 13 additional cuttings yielded four more mixed profiles, but also two samples with a common single‐source profile. The single‐source mtDNA profile matched that of the primary suspect in the case. Thus, even if initial mtDNA analysis yields a mixed profile, a sampling strategy involving multiple locations can improve the chance of obtaining valuable single‐source mtDNA profiles from compromised evidence in criminal casework.     

A Practical Guide for the Formulation of Propositions in the Bayesian Approach to DNA Evidence Interpretation in an Adversarial Environment

The interpretation of complex DNA profiles is facilitated by a Bayesian approach. This approach requires the development of a pair of propositions: one aligned to the prosecution case and one to the defense case. This note explores the issue of proposition setting in an adversarial environment by a series of examples. A set of guidelines generalize how to formulate propositions when there is a single person of interest and when there are multiple individuals of interest. Additional explanations cover how to handle multiple defense propositions, relatives, and the transition from subsource level to activity level propositions. The propositions depend on case information and the allegations of each of the parties. The prosecution proposition is usually known. The authors suggest that a sensible proposition is selected for the defense that is consistent with their stance, if available, and consistent with a realistic defense if their position is not known.     

Establishing the Limits of TrueAllele® Casework: A Validation Study

The limits of the expert system, TrueAllele^® Casework (TA), were explored using challenging mock casework profiles that included 17 single‐source and 18 two‐, 15 three‐ and 7 four‐person DNA mixtures. The sensitivity (ability to detect a minor contributor) of the TA analysis process was examined by challenging the system with mixture DNA samples that exhibited allelic and locus dropout and other stochastic effects. The specificity (ability to exclude nondonors) was rigorously tested by interrogating TA derived genotypes with 100 nondonor profiles. The accuracy with which TA estimated mixture weights of contributors to the two‐person mixtures was examined. Finally, first‐degree relatives of donors were used to assess the ability of the system to exclude close relatives. TA demonstrated great accuracy, sensitivity, and specificity. TA correctly assigned mixture weights and excluded nearly all first‐degree relatives. This study demonstrates the analysis power of the TrueAllele^® Casework system.     

Developmental Validation of the PrepFiler™ Forensic DNA Extraction Kit for Extraction of Genomic DNA from Biological Samples*

Abstract: The PrepFiler? Forensic DNA Extraction Kit enables isolation of genomic DNA from a variety of biological samples. The kit facilitates reversible binding of DNA with magnetic particles resulting in high DNA recovery from samples with very low and high quantities of biological materials: 0.1 and 40 μL of human blood (donor 2) provided 14 and 2883 ng of DNA, respectively. Following the revised SWGDAM guidelines, performance of the developed method was investigated using different sample types including saliva on swabs, semen stains on cotton fabric, samples exposed to environment, samples with polymerase chain reaction (PCR) inhibitors, blood stains (on denim, cotton cloth, and FTA^® paper), and touch evidence‐type samples. DNA yields for all samples tested were equal or better than those obtained by both phenol–chloroform extraction and commercial kits tested. DNA obtained from these samples was free of detectable PCR inhibitors. Short tandem repeat profiles were complete, conclusive, and devoid of PCR artifacts.     

Handwriting evidence evaluation based on the shape of characters: application of multivariate likelihood ratios

A novel Bayesian methodology has been developed to quantitatively assess handwriting evidence by means of a likelihood ratio (LR) designed for multivariate data. This methodology is presented and its applicability is shown through a simulated case of a threatening anonymous text where a suspect is apprehended. The shape of handwritten characters a, d, o, and q of the threatening text was compared with characters of the true writer, and then with two other writers, one with similar and one with dissimilar characters shape compared to the true writer. In each of these three situations, 100 draws of characters were made and the resulting distributions of LR were established to consider the natural handwriting variation. LR values supported the correct hypothesis in every case. This original Bayesian methodology provides a coherent and rigorous tool for the assessment of handwriting evidence, contributing undoubtedly to integrate the field of handwriting examination into science.     

Identification of Human Remains by DNA Analysis of the Gastrointestinal Contents of Fly Larvae

Dipterous fly larvae (maggots) are frequently collected from a corpse during a criminal investigation. Previous studies showed that DNA analysis of the gastrointestinal contents of maggots might be used to reveal the identity of a victim. However, this approach has not been used to date in legal investigations, and thus its practical usefulness is unknown. A badly burned body was discovered with its face and neck colonized by fly larvae. Given the condition of the body, identification was not possible. Short tandem repeat (STR) typing was performed using the gastrointestinal contents of maggots collected from the victim and was compared to STR profiles obtained from the alleged father. The probability of paternity was 99.685%. Thus, this comparative DNA test enabled the conclusive identification of the remains. This is the first reported case of analysis of human DNA isolated from the gastrointestinal tract of maggots used to identify a victim in a criminal case.     

Assessing the potential of bacterial DNA profiling for forensic soil comparisons

A pilot study was undertaken to evaluate DNA profiling of the bacterial community in soil as an alternative to geological methods for forensic soil comparisons. Soil samples from three different ecosystems were compared, and the variation within and between ecologically different sites was determined by using terminal restriction fragment (TRF) analysis of 16S ribosomal DNA. Comparison of TRF profiles revealed that samples from within a specific ecosystem (e.g., a field) showed a significantly higher similarity to each other than to those from another ecosystem (e.g., a forest). In addition, some profile features were unique to specific ecosystems. These features may allow the determination of characteristic profiles that will facilitate identification of ecologically different sites, so that a given sample collected from a suspect could be identified as originating from, for example, a field, rather than a forest. The implications of these preliminary findings for forensic investigations are discussed.     

An Optimized DNA Analysis Workflow for the Sampling,Extraction, and Concentration of DNA obtained from Archived Latent Fingerprints

DNA profiles have been obtained from fingerprints, but there is limited knowledge regarding DNA analysis from archived latent fingerprints—touch DNA “sandwiched” between adhesive and paper. Thus, this study sought to comparatively analyze a variety of collection and analytical methods in an effort to seek an optimized workflow for this specific sample type. Untreated and treated archived latent fingerprints were utilized to compare different biological sampling techniques, swab diluents, DNA extraction systems, DNA concentration practices, and post‐amplification purification methods. Archived latent fingerprints disassembled and sampled via direct cutting, followed by DNA extracted using the QIAamp® DNA Investigator Kit, and concentration with Centri‐Sep? columns increased the odds of obtaining an STR profile. Using the recommended DNA workflow, 9 of the 10 samples provided STR profiles, which included 7–100% of the expected STR alleles and two full profiles. Thus, with carefully selected procedures, archived latent fingerprints can be a viable DNA source for criminal investigations including cold/postconviction cases.     

混合斑的DNA分型解析

综述了常染色体STR、Amelogenin、Y染色体STR、线粒体DNA和单核苷酸多态性等DNA检测方法在解释混合斑检验结果应用中的进展。对混合斑的统计学方法也作了总结。