Effect of incomplete sampling description in DNA reports on bloodstain pattern analysis and reconstruction of a crime scene

Introduction

Physical evidence is extremely important in criminal investigations. During trials, eyewitness testimony is often deemed unreliable or biased, and it is then that physical evidence becomes crucial for the conviction of perpetrators. Crime-scene investigators identify items of interest at a crime scene, and usually items such as bloodstained clothing and footwear are transported to a forensic laboratory for further testing.^1–4

DNA analysts in forensic laboratories are engaged in analysing and sampling bloodstains from bloodstained items. After a suspected stain is observed, analysts determine the nature of the stain using presumptive and confirmatory tests. Several protocols exist in the global forensic community regarding the laboratory processing of DNA evidence, and most of them contain instructions formulated as ‘document the size, location, pattern and condition of the stained area’. ¹ According to protocols, reported descriptions of bloodstains on items should include the size, shape, location and distribution of the stains and, most importantly, a precise description of the type of the sampled bloodstain. DNA analysts have little or no education about patterns of bloodstains, and issues rising from inaccurate descriptions of bloodstains and patterns could occur. Detailed and precise descriptions are very important for subsequent bloodstain pattern analysis (BPA), and we therefore observed and analysed the practical problem of bloodstains in forensic expertise.^5–16

Methods

DNA and BPA reports from our Institute and DNA reports from some of the other forensic laboratories in our country were examined. About 400 reports were observed from the past three years. Only DNA reports related to forensic cases with bloodshed events at crime scenes were included in our detailed observations, and at total of 88 reports were analysed (63 reports from our Institute and 25 reports from other DNA laboratories). Of those 88 reports, 15 reports related to two or more injured people (suspects and victims) and the clothing and/or shoes of those people were subjected to DNA analysis.

First, we analysed descriptions of the items (clothing and shoes) in the DNA reports, and special attention was given to the descriptions of the size, shape, location, distribution and patterns of bloodstains and the descriptions of the sampled bloodstains. Subsequently, we estimated the value of the descriptions of the bloodstained items of interest in linking specific types of bloodstains to the obtained DNA profiles and in final instances to BPA expertise. Based on our experience, the biggest problem exists in cases where two or more people were injured in the same bloodshed event because experts must connect DNA profiles to traces on clothing in order to reconstruct sequence of crime event. So, special attention was paid to those cases.

Results

Of the 88 observed reports, 15 were related to multiple injured people, and the clothing and/or shoes of those people were subjected to DNA analysis. Of those 15 reports, nine were written by experts from our Institute, and six were written by experts from other forensic DNA laboratories in Serbia. DNA reports from our Institute were written by the team of experts who specialised in BPA and molecular biology, and the DNA reports from other forensic laboratories were written exclusively by experts who specialised in molecular biology.

In all nine DNA reports written by the team of experts who specialised in BPA and molecular biology, the clothing and shoes of the people involved in the bloodshed event were described in detailed according to BPA principles (size, shape, location and distribution of bloodstains and identification of specific patterns). Subsequent BPA expertise, based on crime-scene photographs and diagrams, autopsy reports, medical records and DNA reports, could provide very important, complete and specific information for legal authorities. There were no incomplete sampling descriptions in the DNA reports, which could set limitations for BPA expertise.

In all six DNA reports written by experts who specialised in molecular biology, the clothing and shoes of the people involved in the bloodshed event were not described according to BPA principles. Observed descriptions in DNA reports are usually limited to phrases such as ‘the textile of the shirt was blooded at the front, back and sleeves, so several randomly samples were obtained’ or ‘the t-shirt contains several separated bloodstains, so few stains were randomly sampled’ or ‘the trousers were heavily bloodied on the front side and two samples were collected from both legs’ or ‘several types of stains were founded on the upper and lower surface of the left sneaker and two swabs were taken’. The description of every bloodstained item (clothing and shoes) was incomplete or inadequate, and subsequent BPA expertise could not connect every specific type of bloodstain founded on items to the obtained DNA profiles. Those issues in DNA reports set limitations for BPA expertise.

In DNA reports connected with forensic cases where only one person was injured in bloodshed event (54 DNA reports from our Institute and 19 DNA reports from other DNA laboratories), we observed similar phrases for describing bloodstains and patterns on items of interest.

Discussion

According to our observations, DNA analysts who specialise only in molecular biology provide incomplete and insufficient descriptions of bloodstained items in DNA reports. Instead, molecular biologists focus on the identification and individualisation of bloodstains; connecting specific bloodstains and patterns on items of interest to DNA profiles is of less importance for them. Our observations found that this issue developed because molecular biologists in DNA laboratories have little or no education regarding BPA.

If an item of interest has a single stain, there will be no issue for subsequent BPA. In those circumstances, a BPA analyst could analyse the item of interest after DNA investigations have been completed. So, characteristics of the bloodstain could be evaluated, and the mechanisms of origin also could be determined. Issues could occur for BPA expertise if the bloodstain of interest has been heavily damaged or destroyed by the DNA expert.

In forensic cases, heavily bloodied items are often examined featuring several types of contributing bloodstains (i.e. spatter, transfer pattern, wipe, swipe, saturation and flow). If only one person was injured in the bloodshed event and considering the assumption that all bloodstains originate from that person, an incomplete description of bloodstains in the DNA report could be overcome by re-examination of those items by the BPA analyst. However, if bloodstains and patterns on items of interest have been heavily damaged or destroyed during DNA analysis, and if BPA analysts could not determine the types and mechanism of origin for all bloodstain patterns, limitations for subsequent BPA expertise could occur, even when only one blood source exists.^{2–4,6,7,17–21}

A major problem exists in cases where several people were injured in the same event. In those cases, incomplete descriptions of bloodstains in DNA reports could be unhelpful or totally useless for subsequent BPA. In some cases, inadequate descriptions of bloodstained items in DNA reports could be overcome by re-examinations of those items by BPA analysts and sometimes by repeating DNA analysis.^{5–7,9,11,20}

Presented incomplete sampling descriptions set limitations for subsequent BPA and, in the final instance, for reconstructions of a whole crime scene. Our research reveals that knowledge of BPA should be incorporated into the process of sampling bloodstains for DNA analysis. Connecting specific types of bloodstains to obtained DNA profiles is essential for the reconstruction of crime events. The complete analysis should therefore include both a detailed description of all types of observed and sampled bloodstains and linking specific types of bloodstains to the obtained DNA profiles. Such a robust map of different types of bloodstains and corresponding DNA profiles empower analyses of a case and a crime-scene reconstruction.

Experts from our Institute recognised presented problems in DNA reports, which had been reflected in BPA expertise reports of bloodshed crimes. In recent years, we have evaluated more than 400 expertise reports, and we concluded that a problem exists in DNA reports. We defined the problem, which could be overcome by slightly different organisation schemes in forensic laboratories. In order to improve the overall crime-scene investigation and trial process, we highly recommend the implementation of the protocol used in the DNA laboratory at our Institute for the last three years. The protocol was developed by the team of experts of our Institute who specialise in BPA and molecular biology, and it consists of the following key steps:

The team examining bloodstained items consists of both BPA and DNA experts.

Authorities in the forensic science community have different views on signing expertise reports by experts educated in diverse field of forensic science. Also, some of those authorities have different views on the importance and proportion of generalists and specialists experts in the reconstruction process of crime-scene events. The equipment and complex procedures in modern forensic laboratories require more sophisticated knowledge and training, which have led to increased and more detailed specialisation by forensic scientists. Larger laboratories have the privilege of having a wide range of different specialists as a resource available for the generalist scientist to serve as case managers. ²² In DNA laboratories which are part of a larger institute, it would be more appropriate and productive if BPA and DNA experts were to examine bloodstained items cooperatively. Moderately sized laboratories have a limited number of employees. So, in those DNA laboratories, it would be more appropriate to educate DNA analysts in basic principles of BPA, so that they are knowledgeable of the importance of detailed descriptions of bloodstains found and sampled on items of interest.

Recommendations

Based on current research and our previous experience, we highly recommend implementation of at least one of the following steps, given in order of importance:

Examination of bloodstained items and sampling of bloodstains for DNA analysis should be carried out cooperatively by BPA and DNA analysts.

If the first two recommendations are not technically possible in a DNA laboratory or there is management disagreement with our recommendations, at least the third recommendation should be implemented and be mandatory, so that subsequent BPA expertise can provide more useful answers not only to prosecutors and judges but also to attorneys and defence. Our research revealed that between the holistic approach of generalists and narrow areas of specialists a void exists which should be filled by specialists educated in several closely related areas of forensic science. We believe that those specialists represent the future of forensic science, with multiple specialists with different areas of interest being replaced by one specialist trained in the wider area of forensic science.