The interpretation of elemental composition measurements from forensic glass evidence III

In this paper we introduce a permutation testing approach to the interpretation of evidence which consists of elemental composition measurements, with glass evidence as an example. This work extends previous work of Curran et al. [J.M. Curran, C.M. Triggs, J.R. Almirall, J.S. Buckleton and K.A.J. Walsh, The interpretation of elemental composition measurements from forensic glass evidence, Science and Justice 37 (1997) 241–244.] and shows how we may remove some of the constraints that limited the applicability of the previous results. We provide the reader with tools for evidence pre-screening that may aid in the direction of further analyses of the data, rather than for the presentation of evidence interpretation in a court case.     

The importance of forensic evidence for decisions on criminal guilt

Recent studies have found that the general public perceives forensic evidence to be relatively inaccurate and to involve high levels of human judgement. This study examines how important the general public finds forensic evidence by comparing decisions on guilt and punishment in criminal cases that involve forensic versus eyewitness testimony evidence and examining whether a CSI effect exists. Specifically, this experimental survey study utilized a 2 (crime type: murder or rape) × 4 (evidence type: DNA, fingerprint, victim eyewitness testimony, or bystander eyewitness testimony) ? 1 (no victim testimony for murder scenario) design, yielding seven vignettes scenarios to which participants were randomly assigned. Results indicate that forensic evidence was associated with more guilty verdicts and higher confidence in a guilty verdict. Forensic evidence did not change the expected sentence length and did not generally affect the ideal sentence length. However, for rape, respondents believed that the defendant should receive a longer sentence when forensic evidence was presented but forensic evidence did not alter likely sentence that respondents expected the defendant to receive. The results of this study did not support a CSI effect. Overall, this study suggests that forensic evidence – particularly DNA – has a stronger influence during the verdict stage than the sentencing stage.     

When can a DNA profile be regarded as unique?

The probability that a defendant's DNA profile is unique in a population of untyped individuals is shown to be bounded below by one minus twice the sum of the match probabilities over the population. This bound assumes that the possibility of laboratory or handling error can be neglected, and applies only when there is no non-DNA evidence in favour of the defendant. There cannot be a completely general lower bound: if there is overwhelming non-DNA evidence that the defendant is not the source of the crime stain, then that is also overwhelming evidence of non-uniqueness. Application to k-locus short tandem repeat (STR) profiles is discussed, and illustrated with calculations based on the 6-STR-locus system used in current UK casework. However, because of the problem of the non-DNA evidence, there seems to be no satisfactory way for an expert witness to address the question of uniqueness in court.     

Weakening forensic science in Spain: from expert evidence to documentary evidence

An amendment in 2002 to the Spanish Code of Criminal Procedure converted into documentary evidence the expert reports prepared by official laboratories aimed at determining the nature, weight, and purity of seized drugs. In most cases, experts are spared from appearance before the courts. This is likely to be extended to other forensic fields. After an overview of criminalistic identification in current forensic science, the objectivity and reliability concepts used by jurists and scientists are considered by comparing the paradigm of individualization with that of likelihood. Subsequently, a detailed critical study is made on the above-mentioned Spanish legal reform, and a comparison is made with the decision on the Melendez-Diaz v. Massachusetts case as ruled by the Supreme Court of the United States. Although the reform is in compliance with the Spanish Constitution, it is at odds with science, in particular regarding the logic underpinning the scientific evaluation of evidence.     

证据法的法域范围

法庭科学家和证据法学者所处的是两个不同的世界,就像英国和美国一样,由一种共通的语言划分开来。虽然在一些重要方面彼此关联,但法庭科学和证据法学作为两个独立的学科,有着各自独特的构造和演进,关注不同的问题并运用各具特色的认识论。因此,这两个学科之间存在着自说自话的重大风险。该风险的迹象体现在了法庭科学家与证据法学者之间时常沟通不畅。“证据法”的概念对于法庭科学和证据法学而言均至关重要,且在这两个学科中均被高频地运用。本文通过聚焦“证据法的法域范围”之基础概念讨论,希望造成该学科间冲突的个别成因能够明朗化,并诚挚地期盼这样做能有利于法庭科学与证据法学学科之间更有效地交流。     

中国法医学会物证专业委员会法医DNA分析的若干建议

中国法医学会法医物证学专业委员会与国际法医遗传学会中文专委会于2006年10月在成都召开学术会议。我们的讨论强调有必要将国际法医遗传学会的信息及时传递到中国。因此,按照国际法医遗传学会的指南,我们推荐混合斑分析,法医DNA数据库及新遗传标记选择标准供同行参考。     

The statistical interpretation of refractive index measurements II: The multiple source problem

The method proposed by Grove [1] for comparing measurements made on control and recovered fragments is extended to deal with the possibility that the recovered fragments may originally have come from more than one source. The cases of two and four recovered fragments are examined in detail. Simulation results are given which show that the discriminatory power of the method varies with the number of sources and with the distribution of the fragments over those sources. It is greatest when the recovered fragments come from one source.     

A study on the forensic mechanisms of VoIP attacks: Analysis and digital evidence

This paper discusses the use of communication technology to commit crimes, including crime facts and crime techniques. The analysis focuses on the security of voice over Internet protocol (VoIP), a prevention method against VoIP call attack and the attention points for setting up an Internet phone. The importance of digital evidence and digital forensics are emphasised. This paper provides the VoIP digital evidence forensics standard operating procedures (DEFSOP) to help police organisations and establishes an experimental platform to simulate phone calls, hacker attacks and forensic data. Finally, this paper provides a general discussion of a digital evidence strategy that includes VoIP for crime investigators who are interested in digital evidence forensics.     

Understanding juror perceptions of forensic evidence: investigating the impact of case context on perceptions of forensic evidence strength

The most widely accepted model of juror decision making acknowledges the importance of both the case-specific information presented in the courtroom, as well as the prior general knowledge and beliefs held by each juror. The studies presented in this paper investigated whether mock jurors could differentiate between evidence of varying strengths in the absence of case information and then followed on to determine the influence that case context (and therefore the story model) has on judgments made about the strength of forensic DNA evidence. The results illustrated that mock jurors correctly identified various strengths of evidence when it was not presented with case information; however, the perceived strength of evidence was significantly inflated when presented in the context of a criminal case, particularly when the evidence was of a weak or ambiguous standard. These findings are discussed in relation to the story model, and the potential implications for real juries.     

The consequences of potentially differing distributions of the refractive indices of glass fragments from control and recovered sources

In forensic cases involving glass evidence, the variance of the recovered glass refractive index (RI) has been observed to be larger than the variance of the control glass RI. This has consequences for subsequent interpretation. To investigate this phenomenon, a study was made of the probable distributions of refractive indices of the recovered glass given a range of casework type scenarios involving breakage and backscatter. An investigation of the consequences of any distribution differences with regard to casework was also made. It was discovered that the inclusion of surface fragments from the float surface of the glass can have a profound effect on the comparison of recovered and control glass samples. The effect was largest when a breaker was striking the float surface of a window. In particular, it was found that the inclusion of a few surface fragments even post grouping is sufficient by itself to explain the observed differences in variance of RI between control and recovered groups. Surface fragments, if present, are very likely to be treated as outliers and to be deemed as non-matching. The findings of this paper challenge routine glass examination procedure and suggest that knowledge of which surface is facing the striker is valuable information in interpretation.     

The transfer of touch DNA from hands to glass, fabric and wood

The transfer of DNA from hands to objects by holding or touching has been examined in the past. The main purpose of this study was to examine the variation in the amount of DNA transferred from hands to glass, fabric and wood. The study involved 300 volunteers (100 for glass, 100 for fabric and 100 for wood) 50% of which were male and 50% female. The volunteers held the material for 60 s. The DNA was recovered from the objects using a minitape lift, quantified using the Quantifiler kit assay, extracted using a ‘Qiagen^® QIAamp DNA mini kit’ and amplified using the AmpFlSTR^® SGM Plus™ Amplification Kit at 28 cycles. The results show that using ANOVA there was a significant difference (F = 8.2, p < 0.05) between the three object types in the amount of DNA recovered. In terms of DNA transfer and recovery, wood gave the best yield, followed by fabric and then glass. The likelihood of success of obtaining a profile indicative of the holder was approximately 9% for glass samples, 23% for fabric and 36% for wood. There was no significant difference between the amount of DNA transferred by male or female volunteers. In this study good shedder status, as defined by obtaining useful profiles of 6 or more alleles, is estimated at approximately 22% of the population. The phenomenon of secondary transfer was observed when mixed DNA profiles were obtained but the incidence was low at approximately 10% of the total number of samples. DNA profiles corresponding to more than one person were found on objects which had been touched by only one volunteer. Although secondary transfer is possible the profiles obtained from touched objects are more likely to be as a result of primary transfer rather than a secondary source.     

Child abduction murder: the impact of forensic evidence on solvability

This study examined 733 child abduction murders (CAMs) occurring from 1968 to 2002 to explore the influence of forensic evidence on case solvability in CAM investigations. It was hypothesized that the presence of forensic evidence connecting the offender to the crime would enhance case solvability in murder investigations of abducted children. This study examined the impact of CAM of different types of forensic evidence and the impact of the summed total of forensic evidence items on case solvability by controlling for victim age, victim race, victim gender, and victim-offender relationship. Time and distance theoretical predictors were also included. Binomial logistic regression models were used to determine whether forensic evidence was a critical solvability factor in murder investigations of abducted children. This research indicated that, while forensic evidence increased case solvability, the impact of forensic evidence on solvability was not as important as other solvability factors examined.     

Two items of evidence, no putative source: an inference problem in forensic intelligence

Intelligence analysts commonly associate cases on the basis of similarities found in compared characteristics of scientific evidence. The present paper studies some of the inferential difficulties associated with such operations. An analysis is proposed that breaks down the reasoning process into inference to common source, and inference to case linkage. The former requires an approach to the difficulty associated with evaluating the similarities of items of evidence from different cases with no putative source being available. The latter requires consideration to be given to the relevance of evidence. Throughout the paper, probability theory is used to describe the nature of the proposed inferences. Graphical models are also introduced with the aim of providing further insight into the dependence and independence relationships assumed to hold among the various propositions considered. Notions from decision theory are used to discuss ways in which intelligence analysts may assist investigators in deciding whether or not cases should be considered as linked.     

The impact of scavenging:perspective from casework in forensic anthropology

Forensic anthropology casework frequently encounters evidence of animal scavenging asso-ciated with fragmentation and loss of skeletal material.Published resear...     

Forensic identification science evidence since Daubert: Part I--A quantitative analysis of the exclusion of forensic identification science evidence

The U.S. Supreme Court decisions in Daubert v. Merrell Dow Pharmaceuticals Inc. and Kumho Tire Co. Ltd. v. Carmichael transformed the way scientific expert evidence was reviewed in courts across the United States. To gauge the impact of these rulings on the admission of forensic identification evidence, the authors analyzed 548 judicial opinions from cases where admission of such evidence was challenged. Eighty-one cases (15%) involved exclusion or limitation of identification evidence, with 50 (65.7%) of these failing to meet the "reliability" threshold. This was largely because of a failure to demonstrate a sufficient scientific foundation for either the technique (27 cases) or the expert's conclusions (17 cases). The incidence of exclusion/limitation because of a lack of demonstrable reliability suggests that there is a continuing need for the forensic sciences to pursue research validating their underlying theories and techniques of identification to ensure their continued acceptance by the courts.