“Blood,Bucks and Bias”: Reliability and biasability of crime scene investigators’ selection and prioritization of blood traces

When crime scene investigators (CSIs) encounter crime scenes with large volumes of blood, some selection and prioritization is often needed, and this will impact on what blood is and is not available for forensic analysis. What factors influence CSIs decision making process is largely unknown. This study examines the effects of awareness of limited resources and irrelevant contextual case information indicating either a homicide or a suicide on CSIs collection of blood traces. To this end, two scenario-based experiments with CSIs and novices were conducted. Overall, the results suggest that even when CSIs decisions are made under identical conditions, their trace selection varies both when it comes to numbers and locations. Furthermore, awareness of limited resources made CSIs collect fewer traces and their selections also varied following the contextual case information, showing similarities and differences with novices. Since blood traces can be used to establish both activity and identity the findings can have important implications for the subsequent investigation as well as trial.     

The Forensic Confirmation Bias: A Comparison Between Experts and Novices

A large body of research has described the influence of context information on forensic decision‐making. In this study, we examined the effect of context information on the search for and selection of traces by students (N = 36) and crime scene investigators (N = 58). Participants investigated an ambiguous mock crime scene and received prior information indicating suicide, a violent death or no information. Participants described their impression of the scene and wrote down which traces they wanted to secure. Results showed that context information impacted first impression of the scene and crime scene behavior, namely number of traces secured. Participants in the murder condition secured most traces. Furthermore, the students secured more crime‐related traces. Students were more confident in their first impression. This study does not indicate that experts outperform novices. We therefore argue for proper training on cognitive processes as an integral part of all forensic education.     

Targeting relevant sampling areas for human biological traces: Where to sample displaced bodies for offender DNA?

Sampling strategy is one of the deciding factors in DNA typing success rates. Small amounts of bodily fluid traces and (skin) contact traces are currently not visualized in standard forensic practice. Trace recovery is usually based on the information available in a particular case and on the experience and ‘forensic common sense’ applied by the trace recovery expert. Interactions between an offender and a victim may have characteristic features, resulting in specific trace patterns. Understanding these interactions, and their resulting trace patterns, might improve crime related trace recovery as well as DNA typing success rates.In this study, we examined the interactions between offender and victim when a body has been relocated from one position/location to another. The contact between the hands of the offender and the body of the victim was visualized using a fluorescent dye in a lotion that was applied to the hands of the individual undertaking the relocation. The contact locations were scored and patterns were analyzed based on both victim and offender characteristics (height, weight, age, gender). The resulting patterns were compared to current trace recovery practices in the Netherlands. The results of this large-scale study facilitate evidence-based sampling supporting both investigative and evaluative forensic examinations.     

Naturalistic decision making in forensic science: toward a better understanding of decision making by forensic team leaders

This study uses the naturalistic decision-making (NDM) perspective to examine how Dutch forensic team leaders (i.e., the officers in charge of criminal forensic research from the crime scene until the use of laboratory assistance) make decisions in real-life settings and identifies the contextual factors that might influence those decisions. First, a focus group interview was conducted to identify four NDM mechanisms in day-to-day forensic decision making. Second, a serious game was conducted to examine the influence of three of these contextual mechanisms. The results uncovered that forensic team leaders (i) were attracted to obtain further information when more information was initially made available, (ii) were likely to devote more attention to emotionally charged cases, and (iii) used not only forensic evidence in the decision making but also tactical, unverified information of the police inquiry. Interestingly, the measured contextual influences did not deviate significantly from a control group of laypeople.     

DNA in the Criminal Justice System: The DNA Success Story in Perspective,

Current figures on the efficiency of DNA as an investigative tool in criminal investigations only tell part of the story. To get the DNA success story in the right perspective, we examined all forensic reports from serious (N = 116) and high‐volume crime cases (N = 2791) over the year 2011 from one police region in the Netherlands. These data show that 38% of analyzed serious crime traces (N = 384) and 17% of analyzed high‐volume crime traces (N = 386) did not result in a DNA profile. Turnaround times (from crime scene to DNA report) were 66 days for traces from serious crimes and 44 days for traces from high‐volume crimes. Suspects were truly identified through a match with the Offender DNA database of the Netherlands in 3% of the serious crime cases and in 1% of the high‐volume crime cases. These data are important for both the forensic laboratory and the professionals in the criminal justice system to further optimize forensic DNA testing as an investigative tool.     

The future of forensic and crime scene science. Part I. A UK forensic science user and provider perspective

This paper presents an overview of the views expressed by UK forensic science users and providers during the Centre for Forensic Investigation's 1 day conference 'The Future of Forensic and Crime Scene Science' and is set in the context of the changing national agenda and likely advances in current and future technology. It begins by examining the success of the Home Office DNA Expansion Programme and future demands of the Criminal Justice System, highlighting the changing use of forensic science both at the crime scene and within the forensic process itself. In particular, the use of forensic science at the early stages of an investigation to provide intelligence and support the decision making process is discussed together with the need to adopt a partnership approach to tackling crime and its causes. Key system and technological drivers for performance improvement and change are identified and the likely timescales and implications of their introduction are discussed. Finally, the Home Office plans to build on the success of the DNA Expansion Programme, through the introduction of the proposed Home Office Forensic Integration Strategy, are explored and the paper concludes by highlighting the benefits, implications and issues arising from the changing and developing use of forensic science.     

Analysis of mitochondrial SNPs in addition to conventional STR-typing in a case of aggravated theft

In the field of forensic DNA typing, the analysis of Short Tandem Repeats (STRs) can fail in cases of degraded DNA. The typing of coding region Single Nucleotide Polymorphisms (SNPs) of the mitochondrial genome provides an approach to acquire additional information. In the examined case of aggravated theft, both suspects could be excluded of having left the analyzed hair on the crime scene by SNP typing. This conclusion was not possible subsequent to STR typing. SNP typing of the trace on the torch light left on the crime scene increased the likelihood for suspect no. 2 to be the origin of this trace. This finding was already indicated by STR analysis. Suspect no. 1 was excluded for being the origin of this trace by SNP typing which was also indicated by STR analysis. A limiting factor for the analysis of SNPs is the maternal inheritance of mitochondrial DNA. Individualisation is not possible. In conclusion, it can be said that in the case of traces which cause problems with conventional STR typing the supplementary analysis of coding region SNPs from the mitochondrial genome is very reasonable and greatly contributes to the refinement of analysis methods in the field of forensic genetics.     

The Influence of New Technologies on the Visual Attention of CSIs Performing a Crime Scene Investigation

Currently, a series of promising new tools are under development that will enable crime scene investigators (CSIs) to analyze traces in situ during the crime scene investigation or enable them to detect blood and provide information on the age of blood. An experiment is conducted with thirty CSIs investigating a violent robbery at a mock crime scene to study the influence of such technologies on the perception and interpretation of traces during the first phase of the investigation. Results show that in their search for traces, CSIs are not directed by the availability of technologies, which is a reassuring finding. Qualitative findings suggest that CSIs are generally more focused on analyzing perpetrator traces than on reconstructing the event. A focus on perpetrator traces might become a risk when other crime‐related traces are overlooked, and when analyzed traces are in fact not crime‐related and in consequence lead to the identification of innocent suspects.     

Heat and let dye: Part II – Rapid heat-fixing of blood traces

Blood-contaminated shoeprints and footmarks contain valuable operational information as they may bind an individual who stepped in the crime scene with the incident and not merely with the location. As determining the age of a bloodstain remains a challenge, while processing the scene, it is difficult to determine whether the blood is completely, or partially, dry. Thus, executing a dye staining protocol may wash these marks away as they might still be soluble. However, to meet this challenge, it is possible to fix blood marks using heat. This study aims to find a solution for floor surfaces covered by heavier blood traces (shoeprints and footmarks). For this purpose, a new pseudo-operating device was constructed for examining the blood-fixing process of both mentioned trace types. Two trials were performed with depletion marks. The results revealed that fully developed fresh and heavily blood deposits were obtained by heating to 200°C for 7.5 min using the fixing device, followed by a staining protocol using amido black solution. The achieved sharp resolution of the examined bloody prints demonstrates that in certain cases the dehydration mechanism of heating is preferred over precipitating the proteins attributed to 5-sulfosalycilic acid; thus, reducing the risk of washing blood evidence while processing the crime scene.     

The Use of Adhesive Tape for Recovery of DNA from Crime Scene Items

Abstract: The selection of the appropriate method of collection of biological material from crime scene items can be crucial to obtaining a DNA profile. The three techniques commonly used for sampling items are: cutting, swabbing, and taping. The tape sampling technique offers an advantage, in that it enables the collection of a potentially highly informative source of DNA, shed epithelial cells, from selected areas on crime scene items (the inside fingers of a glove, for instance). Furthermore, surface collection of biological material by taping reduces co‐sampling of known PCR inhibitors such as clothing dyes. The correct choice of tape for crime scene item sampling is important. Not all tapes are suitable for biological trace evidence collection as well as DNA extraction. We report on one tape that met both these criteria. Three different cases are presented which demonstrate the usefulness of adhesive tape sampling of crime items. Finally, the advantages of the tape collection technique are discussed and guidelines for preferred areas of tape sampling on various casework items are presented.     

微量生物物证提取套装在现场微量血痕DNA检验中的应用

目的探讨微量生物物证提取套装应用于提取现场微量血痕DNA的检验效果。方法将静脉血制成地面血痕。分别应用微量生物物证提取套装法和普通法提取血痕。分别于恒温摇床放置2、24、48、72、96h(每组50份)进行血痕DNA检验,对比各组检验结果。结果恒温摇床上分别放置24、48、72、96h后,微量生物物证提取套装法的DNA检出率(分别为100.00%、100.00%、100.00%、96.00%)均高于普通法(分别为62.00%、26.00%、10.00%、0),差异均具有统计学意义(P<0.05)。恒温摇床上放置2h,两种方法的DNA检出率差异无统计学意义(P>0.05)。结论微量生物物证提取套装可有效提升放置时间较久的现场微量血痕的检出率和检出时限。     

The use of the M-Vac® wet-vacuum system as a method for DNA recovery

Collecting sufficient template DNA from a crime scene sample is often challenging, especially with low quantity samples such as touch DNA (tDNA). Traditional DNA collection methods such as double swabbing have limitations, in particular when used on certain substrates which can be found at crime scenes, thus a better collection method is advantageous. Here, the effectiveness of the M-Vac® Wet-Vacuum System is evaluated as a method for DNA recovery on tiles and bricks. It was found that the M-Vac® recovered 75% more DNA than double swabbing on bricks. However, double swabbing collected significantly more DNA than the M-Vac® on tiles. Additionally, it was found that cell-free DNA is lost in the filtration step of M-Vac® collection. In terms of peak height and number of true alleles detected, no significant difference was found between the DNA profiles obtained through M-Vac® collection versus double swabbing of tDNA depositions from 12 volunteers on bricks. The results demonstrate that the M-Vac® has potential for DNA collection from porous surfaces such as bricks, but that alterations to the filter apparatus would be beneficial to increase the amount of genetic material collected for subsequent DNA profiling. These results are anticipated to be a starting point to validate the M-Vac® as a DNA collection device, providing an alternative method when DNA is present on a difficult substrate, or if traditional DNA collection methods have failed.     

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。     

A forensic science perspective on the role of images in crime investigation and reconstruction

This article presents a global vision of images in forensic science. The proliferation of perspectives on the use of images throughout criminal investigations and the increasing demand for research on this topic seem to demand a forensic science-based analysis. In this study, the definitions of and concepts related to material traces are revisited and applied to images, and a structured approach is used to persuade the scientific community to extend and improve the use of images as traces in criminal investigations. Current research efforts focus on technical issues and evidence assessment. This article provides a sound foundation for rationalising and explaining the processes involved in the production of clues from trace images. For example, the mechanisms through which these visual traces become clues of presence or action are described. An extensive literature review of forensic image analysis emphasises the existing guidelines and knowledge available for answering investigative questions (who, what, where, when and how). However, complementary developments are still necessary to demystify many aspects of image analysis in forensic science, including how to review and select images or use them to reconstruct an event or assist intelligence efforts. The hypothetico-deductive reasoning pathway used to discover unknown elements of an event or crime can also help scientists understand the underlying processes involved in their decision making. An analysis of a single image in an investigative or probative context is used to demonstrate the highly informative potential of images as traces and/or clues. Research efforts should be directed toward formalising the extraction and combination of clues from images. An appropriate methodology is key to expanding the use of images in forensic science.     

Simply Criminal: Predicting Burglars’ Occupancy Decisions with a Simple Heuristic

Rational choice theories of criminal decision making assume that offenders weight and integrate multiple cues when making decisions (i.e., are compensatory). We tested this assumption by comparing how well a compensatory strategy called Franklin’s Rule captured burglars’ decision policies regarding residence occupancy compared to a non-compensatory strategy (i.e., Matching Heuristic). Forty burglars each decided on the occupancy of 20 randomly selected photographs of residences (for which actual occupancy was known when the photo was taken). Participants also provided open-ended reports on the cues that influenced their decisions in each case, and then rated the importance of eight cues (e.g., deadbolt visible) over all decisions. Burglars predicted occupancy beyond chance levels. The Matching Heuristic was a significantly better predictor of burglars’ decisions than Franklin’s Rule, and cue use in the Matching Heuristic better corresponded to the cue ecological validities in the environment than cue use in Franklin’s Rule. The most important cue in burglars’ models was also the most ecologically valid or predictive of actual occupancy (i.e., vehicle present). The majority of burglars correctly identified the most important cue in their models, and the open-ended technique showed greater correspondence between self-reported and captured cue use than the rating over decision technique. Our findings support a limited rationality perspective to understanding criminal decision making, and have implications for crime prevention.     

Female criminals—It's not always the offender!

Numerous crimes (including murder), all having a common denominator, occurred in Germany and Austria between 1993 and 2009. All of these cases presented with identical female DNA traces being found at the crime scene. The crimes committed differed markedly, as did the suspects involved, which were of varied origin. Many of these cases could be solved. However, none of the suspects could identify an involved female. Fourteen of these cases (including one murder) occurred in Upper Austria.A special task force of the Austrian police, together with the Institute of Legal Medicine in Salzburg, began systematically searching for errors in the investigative process after the cases became more and more incoherent and nebulous. In the end, the DNA trace evidence was shown to be contaminated. A woman involved in the manufacture of the cotton swabs turned out to be the source of the female DNA profile.Following this, several products of other manufacturers were tested for contamination with DNA. It was noted that cotton swabs which had been sterilised with radiation were often contaminated. As a result, it is recommended that the manufacturing process, as well as the products themselves used in collection of DNA trace evidence, should be re-evaluated with the emphasis on preventing contamination.     

DNA investigative lead development from blood and saliva samples in less than two hours using the RapidHIT™ Human DNA Identification System

The RapidHIT™ Human DNA Identification System produces full STR DNA profiles (sample in, results out) in 90 min. Here we present results from a new protocol on the RapidHIT System, designed for crime scene samples. Data are presented for blood and saliva samples, with results for a range of samples and substrates. Success rates and sensitivity display a high level of performance for the sample types evaluated in the study and demonstrate the efficacy of the new protocol for crime scene samples.     

In search of reasonable doubt

A number of different approaches have been used to quantify jurors' use of the decision criterion known as reasonable doubt. The purpose of the present study was to determine which of a select group of these approaches could be utilized to match the actual decisions of individuals role-playing jurors for an assault trial. Simon's (1970) rank-order approach, a self-report approach, an approach derived from Statistical Decision Theory (Fried, Kaplan, & Klein, 1975), and one derived from Justice White's explanation of theJohnson v. Louisiana (1972) decision were each used to estimate values for reasonable doubt. The estimates were then used to recreate the individual decisions, and the recreated decisions were then compared to the actual decisions. The results indicated that every approach accurately matched the actual decisions at a better-than-chance rate, although the rank-order and decision theory approaches were most accurate. The reasonable doubt estimates obtained from each of the approaches were also used to examine the basic assumption underlying the Thomas and Hogue (1976) juror decision model. Only the estimates from the decision theory approach provided consistent support for the assumption. A variety of methods were suggested for more definite determinations of the accuracy of the approaches tested, and the relative merits of the approaches were discussed.     

Evaluation of amylase testing as a tool for saliva screening of crime scene trace swabs

Amylase testing has been used as a presumptive test for crime scene saliva for over three decades, mainly to locate saliva stains on surfaces. We have developed a saliva screening application for crime scene trace swabs, utilising an amylase sensitive paper (Phadebas^® Forensic Press test). Positive results were obtained for all tested dried saliva stains (0.5–32 μL) with high or intermediate amylase activity (840 and 290 kU/L). Results were typically obtained within 5 min, and all samples that produced DNA profiles were positive. However, salivary amylase activities, as well as DNA concentrations, vary significantly between individuals. We show that there is no correlation between amylase activity and amount of DNA in fresh saliva. Even so, a positive amylase result indicates presence of saliva, and thereby presence of DNA. Amylase testing may be useful for screening in investigations where the number of DNA analyses is limited due to cost, e.g., in volume crime.     

DNA Databases as Alternative Data Sources for Criminological Research

DNA traces found at crime scenes and DNA records held in databases have already helped the police to solve numerous investigations into specific crimes. The police clearly benefit from the use of forensic science at an operational (i.e. case) level. This paper focuses on the use of forensic DNA at a strategic level: its use in the study of patterns of criminal behaviour. The usual sources of information for this type of research are recorded crime data, self-report studies and victimization surveys. However, as our review will show, these data sources cannot provide a complete picture of crime. We therefore propose an alternative approach to criminological research that takes into account DNA databases and has the potential to augment current methods and extend the existing knowledge beyond known offenders. The use of DNA databases has an important advantage for criminological research: it is possible to link offences committed by the same individual, whether the offender’s identity is known or not. By making a one-on-one comparison of police data with the corresponding DNA data, not only can co-offenders be studied, but a larger network of offenders connected to each other can also be analysed, even if their identity is unknown to the police.