Quantitative assessment of evidential weight for a fingerprint comparison. Part II: a generalisation to take account of the general pattern

The authors have proposed a quantitative method for assessing weight of evidence in the case where a fingermark from a crime scene is compared with a set of control prints from the ten fingers of a suspect. The approach is based on the notion of calculating a Likelihood Ratio (LR) that addresses a pair of propositions relating to the individual who left the crime mark. The current method considers only information extracted from minutiae, such as location, direction and type. It does not consider other information usually taken into account by fingerprint examiners, such as the general pattern of the ridge flow on the mark and the control prints. In this paper, we propose an improvement to our model that allows a fingerprint examiner to take advantage of pattern information when assessing the evidential weight to be assigned to a fingerprint comparison. We present an extension of the formal analysis proposed earlier and we illustrate our approach with an example.     

Likelihood ratio methods for forensic comparison of evaporated gasoline residues

In the investigation of arson, evidence connecting a suspect to the fire scene may be obtained by comparing the composition of ignitable liquid residues found at the crime scene to ignitable liquids found in possession of the suspect. Interpreting the result of such a comparison is hampered by processes at the crime scene that result in evaporation, matrix interference, and microbial degradation of the ignitable liquid.Most commonly, gasoline is used as a fire accelerant in arson. In the current scientific literature on gasoline comparison, classification studies are reported for unevaporated and evaporated gasoline residues. In these studies the goal is to discriminate between samples of several sources of gasoline, based on a chemical analysis. While in classification studies the focus is on discrimination of gasolines, for forensic purposes a likelihood ratio approach is more relevant.In this work, a first step is made towards the ultimate goal of obtaining numerical values for the strength of evidence for the inference of identity of source in gasoline comparisons. Three likelihood ratio methods are presented for the comparison of evaporated gasoline residues (up to 75% weight loss under laboratory conditions). Two methods based on distance functions and one multivariate method were developed. The performance of the three methods is characterized by rates of misleading evidence, an analysis of the calibration and an information theoretical analysis.The three methods show strong improvement of discrimination as compared with a completely uninformative method. The two distance functions perform better than the multivariate method, in terms of discrimination and rates of misleading evidence.     

Unusual contact marks: connecting the hubcap to the wheel of the car

A case of homicide and attempted homicide is described. The comparison of tire-marks linked the suspect's vehicle to the scene of crime only with low certainty. However, the comparison of the pressure mark on the hubcap found at the scene, with the balance weight on one of the wheels of the suspect's car, connected the suspect to the scene of crime with high certainty.     

Pollen on grass clippings: putting the suspect at the scene of the crime.

In a case of alleged sexual assault, the pollen content of samples of grass clippings and soil from the suspect's clothing and shoes was compared to that of a sample of grass clippings from the alleged crime scene (a grassy area) to determine whether or not the suspect had been at the scene. The clothing and shoe samples showed a very strong correlation with each other and with the sample from the alleged crime scene in the combination of the different types of pollen present, very strongly supporting the contention that the suspect had been at the scene.     

Palynology and mycology as biological evidence in a homicide case

Criminal cases are studied from several disciplines to link a suspect with a criminal act. In this case, a man was reported missing in a coastal area in Buenos Aires Province, Argentina. The victim's relatives pointed to a possible suspect, and the local police carried out the investigation. We contributed to this research by applying palynological and mycological techniques. Palynomorphs and fungal spores offer valuable trace evidence, as they can be easily transferred between objects and crime scenes due to their minute size and persist on them for a long time. The victim was found 25 days later, lying on sandy soil, which partially covered the body, 35 km from where the suspect was arrested. Comparative samples were collected from the crime scene and the suspect's home and belongings (clothes, footwear, and seized vehicle). The palynological associations obtained from the crime scene and the defendant's belongings were dominated by diatoms and acritarchs (Acantomorphitae), all elements of marine origin, and a high CFU number of Bipolaris cynodontis, which allowed the defendant's clothing to be related to the place of corpse discovery. Soil from the defendant's home had an entirely continental composition, and the fungal biota was characteristic of prairie areas which were different from those of the crime scene.     

Forensic entomology exemplified by a homicide. A combined stain and postmortem time analysis]

The combined analysis of both ant and blow fly evidence recovered from a corpse, and from the boot of a suspect, suggested that an assumed scenario in a high profile murder case was likely to be true. The ants (Lasius fuliginous) were used as classical crime scene stains that linked the suspect to the scene. Blow fly maggots (Calliphora spec.) helped to determine the post mortem interval (PMI) with the calculated PMI overlapping with the assumed time of the killing. In the trial, the results of the medico-legal analysis of the insects was understood to be crucial scientific evidence, and the suspect was sentenced to 8 years in prison.     

Evidence evaluation in fingerprint comparison and automated fingerprint identification systems--modelling within finger variability

Recent challenges and errors in fingerprint identification have highlighted the need for assessing the information content of a papillary pattern in a systematic way. In particular, estimation of the statistical uncertainty associated with this type of evidence is more and more called upon. The approach used in the present study is based on the assessment of likelihood ratios (LRs). This evaluative tool weighs the likelihood of evidence given two mutually exclusive hypotheses. The computation of likelihood ratios on a database of marks of known sources (matching the unknown and non-matching the unknown mark) allows an estimation of the evidential contribution of fingerprint evidence. LRs are computed taking advantage of the scores obtained from an automated fingerprint identification system and hence are based exclusively on level II features (minutiae). The AFIS system attributes a score to any comparison (fingerprint to fingerprint, mark to mark and mark to fingerprint), used here as a proximity measure between the respective arrangements of minutiae. The numerator of the LR addresses the within finger variability and is obtained by comparing the same configurations of minutiae coming from the same source. Only comparisons where the same minutiae are visible both on the mark and on the print are therefore taken into account. The denominator of the LR is obtained by cross-comparison with a database of prints originating from non-matching sources. The estimation of the numerator of the LR is much more complex in terms of specific data requirements than the estimation of the denominator of the LR (that requires only a large database of prints from an non-associated population). Hence this paper addresses specific issues associated with the numerator or within finger variability. This study aims at answering the following questions: (1) how a database for modelling within finger variability should be acquired; (2) whether or not the visualisation technique or the choice of different minutiae arrangements may influence that modelling and (3) what is the magnitude of LRs that can be expected from such a model. Results show that within finger variability is affected by the visualisation technique used on the mark, the number of minutiae and the minutiae configuration. They also show that the rates of misleading evidence in the likelihood ratios obtained for one of the configurations examined are low.     

植物DNA检验技术在命案现场重建中的应用策略

植物DNA检验技术是利用植物遗传性状的稳态性对关联植物物证进行检验鉴定的手段。将该技术应用于现场重建,应基于植物物证与犯罪嫌疑人、被害人及其活动环境具有＂重大关联性＂。从命案现场重建的需求上看,应围绕犯罪嫌疑人及其可控物品中附着植物与现场植物的种属同一性判断、被害人尸体（尸块或尸骸）及其随附物品中附着植物与中心现场植物的种属同一性判断、疑似侵害物及其附着植物与嫌疑人行为关联植物的种属同一性判断等三个角度或层次进行检验和综合分析。植物DNA检验技术可阐明物证的时空运行停顿规律,为命案现场重建工作提供一种参考性解决方案。     

Use of fecal material to associate a suspect with a crime scene: report of two cases

Fecal matter analyses were applied to two cases: a homicide and a robbery. Scrapings of fecal matter removed from samples of clothing obtained from a homicide suspect were examined for their plant cell and cell fragment content and compared with fecal matter from a rape-homicide victim and scrapings from her clothing. Scrapings were hydrated and examined microscopically. Types of food plants were identified from the observed cells by comparison with known food plants. A similar analysis was conducted on the clothing of a robbery suspect and compared with fecal material left at the crime scene. The results showed that, respectively in the two cases, the reference samples were remarkably similar, if not identical, to those from the suspects' clothing.     

Fingermark Evidence Evaluation Based on Automated Fingerprint Identification System Matching Scores: The Effect of Different Types of Conditioning on Likelihood Ratios

In recent studies, the evidential value of the similarity of minutiae configurations of fingermarks and fingerprints, for example expressed by automated fingerprint identification systems (AFIS), is determined by likelihood ratios (LRs). The paper explores whether there is an effect on LRs if conditioning takes place on specified fingers, fingerprints, or fingermarks under competing hypotheses: In addition, an approach is explored where conditioning is asymmetric. Comparisons between fingerprints and simulated fingermarks with eight minutiae are performed to produce similarity score distributions for each type of conditioning, given a fixed AFIS matching algorithm. Both similarity scores and LRs are significantly different if the conditioning changes. Given a common‐source scenario, “LRs” resulting from asymmetric conditioning are on average higher. The difference may reach a factor of 2000. As conditioning on a suspect's finger(print) is labor‐intensive and requires a cooperating suspect, it is recommended to just condition on the number of minutiae in the fingermark.     

犯罪现场层次论

犯罪现场层次是犯罪现场存在表现及其被侦查人员认知的程度。犯罪现场是由犯罪时间、犯罪空间、犯罪嫌疑人条件、犯罪痕迹物证、犯罪活动过程、犯罪心理、犯罪证据等各种层次构成的复合体。研究犯罪现场层次论也是研究犯罪现场构成要素的存在及其在不同层面的联系。犯罪现场层次也是研究和揭示犯罪现场存在的一种认知。研究犯罪现场层次问题,也可以使我们对犯罪现场状况及其勘查工作质量给以程度判定。     

Photographic Image Comparison of Vegetation

Images and videos are common types of evidence in crime scene investigations and laboratory analysis. Images may be taken by the suspect and/or by crime scene investigators and may serve as crucial elements in forensic laboratory analysis. Forensic photographic image comparison is the process of comparing one or more objects or persons in photographs/images when at least one image is known to be related to a crime. The forensic examiner usually compares the images in order to determine whether or not an association between the exhibits in the images can be made. This paper proposes an extension to the currently prevalent photographic image examination method. The extension introduces comparison of landscape and vegetation over time. It is revealed that similarities between images may still be found between the period of time the suspect photograph was taken and the period the crime scene investigator took the photograph from the same area. In this case report, two suspects to be involved in growing a marijuana field were arrested by the police. The forensic experts were asked to examine images taken by the crime scene investigators and to compare them to the images found in the suspects’ phones. They then tried to determine whether the suspects could be linked to the specific locations. While applying techniques derived from morphological comparison methodologies, the plants at the scene provided significant additional information. A tree trunk, branches, and twigs on a hedge in the photographs revealed specific individual characteristics that led the examiner to reach a conclusive decision.     

Forensic Investigation of a Shawl Linked to the “Jack the Ripper” Murders

A set of historic murders, known as the “Jack the Ripper murders,” started in London in August 1888. The killer's identity has remained a mystery to date. Here, we describe the investigation of, to our knowledge, the only remaining physical evidence linked to these murders, recovered from one of the victims at the scene of the crime. We applied novel, minimally destructive techniques for sample recovery from forensically relevant stains on the evidence and separated single cells linked to the suspect, followed by phenotypic analysis. The mtDNA profiles of both the victim and the suspect matched the corresponding reference samples, fortifying the link of the evidence to the crime scene. Genomic DNA from single cells recovered from the evidence was amplified, and the phenotypic information acquired matched the only witness statement regarded as reliable. To our knowledge, this is the most advanced study to date regarding this case.     

犯罪剖绘:科学还是艺术?

犯罪剖绘(criminal profiling)为分析(连续)犯罪行为型态的技术,藉由统计技术分析潜在犯罪者、被害者与犯罪现场迹证等三者之间相互联结可能性。然犯罪剖绘技术应用至案件连结分析,可根据犯罪现场所遗留迹证(含心理迹证),预测/推论犯罪者之人口背景特征,并将这些案件之犯罪现场迹证系统化处理,建构成数据库,有助警察侦办连续型犯罪。经由案件连结分析所得证据,能否成为法庭上论罪之依据,在英美国家必须通过Frye法则与Daubert测试法则检验,即是否已经通过科学性检验,或同一学术领域同侪认可验证过程。因此,后续研究可朝更精确统计分析方法迈进,以提升案件连结分析数据库对于预测未发现犯罪者之准确率及其法庭证据力。     

采用纯CO气体杀人案件的分析

一氧化碳(CO)气体中毒致人死亡多见于自杀和意外事件,采用纯CO气体杀人的案例国内罕有报道。本文报道了一起采用瓶装纯CO气体致人中毒死亡的案例,作案方式隐蔽,作案手段鲜见,且伪造了作案现场,给侦查带来一定困难。经刑事技术人员认真细致地现场勘查、尸体检验和物证提取检验,结合调查访问,最终明确了案件性质,认定了犯罪嫌疑人,全面还原了其作案过程。笔者总结分析了该案刑事技术工作中的要点和难点,希望能对同行们有所帮助。     

用改性热塑性树脂制模提取立体痕迹的研究

目的提出一种采用改性热塑性树脂来提取案发现场立体痕迹的新方法。方法利用市场上常见的热塑性高分子合成树脂,通过对其熔融流动性及指数的改变,使之能适应提取立体痕迹的需要,并与常用的硅橡胶提取材料的性能测试数据进行了分析比较。结果该方法提取的立体痕迹模型反映细微特征明显。结论操作方法简便快捷,性能更为优越,易于收藏保存。     

A novel approach for fingerprinting mummified hands

Abstract:  Fingerprinting has long been used as a method for identifying bodies and, since first discovered, many advances have been made in both fingerprint acquisition and interpretation. However, in the field of forensic pathology, the attainment of fingerprints from mummified bodies has remained difficult. The most common technique historically used to obtain fingerprints in these cases usually employs the amputation of the fingers combined with soaking and/or injecting the fingers with various solutions in order to enhance the fingerprints. A novel approach to fingerprinting mummified fingers is presented which involves removal and rehydration of the fingerpads (including the epidermal, dermal, and adipose tissues) followed by inking and rolling, using a gloved finger for support. The technique presented produces a superior quality of print without amputation of the finger, yielding excellent results and assisting in obtaining positive identification.     

Interpreting small quantities of DNA: the hierarchy of propositions and the use of Bayesian networks

The dramatic increase in the sensitivity of DNA profiling systems that has occurred over recent years has led to the need to address a wider range of interpretational problems in forensic science. The issues surrounding questions of the kind "whose DNA is this?" have been the subject of considerable controversy but now it is clear that the emphasis is shifting to questions of the kind "how did this DNA get here?" Such issues are discussed in this paper and new insights are provided by two particular recent developments. First, the notion of the "hierarchy of propositions" that has arisen from a project called Case Assessment and Interpretation (CAI) that has been running in the British Forensic Science Service (FSS). Second, a technique for drawing inferences in the face of many interacting considerations, known as "Bayesian networks"--or "Bayes' nets" for short--that has been the subject of an earlier paper in this journal (1). The discussion is carried out by means of case studies, based on actual cases. It is clear that, whereas the inference in relation to the source of the DNA in a crime sample might be overwhelmingly strong, the inference in relation to the propositions that a jury must consider relating to the identity of the actual offender may be much more tentative.     

Inclusion Probabilities and Dropout

Abstract: Recent discussions on a forensic discussion group highlighted the prevalence of a practice in the application of inclusion probabilities when dropout is possible that is of significant concern. In such cases, there appears to be an unpublished practice of calculation of an inclusion probability only for those loci at which the profile of interest (hereafter the suspect) is fully included among the alleles present in the crime scene sample and to omit those loci at which the suspect has alleles that are not fully represented among the alleles in the mixture. The danger is that this approach may produce apparently strong evidence against a surprisingly large fraction of noncontributors. In this paper, the risk associated with the approach of ignoring loci with discordant alleles is assessed by simulation.     

Distribution of the minutiae in the fingerprints of a sample of the Spanish population

One of the fundamental aspects of the process of identification through fingerprints is the comparison of the minutiae between the fingermark obtained at the scene of the crime and the suspect's corresponding finger. There is no scientific basis in this process that allows the use of numerical standards, such as those kept in different countries, to obtain the identification. The recent mistakes made in the field of dactyloscopy, together with the growing rigor and scrutiny that forensic evidence undergoes in the legislative and scientific areas, have resulted in the need to reconsider some of the basic principles that support this discipline. A probabilistic estimation of the evidential value is especially necessary; therefore, it is indispensable to know and quantify the variability of the features used in the identification process. The sample studied for this research was obtained from 100 Caucasian men and 100 Caucasian women from the Spanish population, which amounts to a total of 2000 fingerprints. The different types of minutiae were located, identified, and quantified visually on the fingerprint, in four sectors, and inside and outside of a circle, whose radius cut, perpendicularly, fifteen ridges starting from the center cut of the axes that defined the sectors. According to the results obtained in this study, through dactyloscopic identification, the weight of the evidence of a minutia, such as the ridge endings, with frequencies between 55% and 65%, according to the area and gender evaluated, cannot be the same as that of a bifurcation or convergence, with frequencies of 13-18% or those of other minutiae that show frequencies lower than 3%. The significant differences found in the topological distribution of the endings, bifurcations, and convergences show the need to take into account, for its demonstrational value, the finger area in which they are evaluated. The significant association observed between the types of minutiae and the different fingers revealed a greater frequency of endings on the thumb and index fingers, and bifurcations and convergences on the middle, ring, and little fingers.