Hebelwerkzeuge als Spurenträger

Tools as trace evidence carriers are gaining increasing interest in forensic DNA analysis. A significant increase in lever traces can be observed in the material analyzed by the Homburg Institute. Against this background, the aim of this study is to develop a rationally based concept for crime scene work.

In the first step, the DNA content of corresponding traces was systematically determined experimentally: Two test subjects used 6 different lever tools (4 screwdrivers, 2 nail pullers) to make lever marks on 3 windows of different material types (wood, aluminium, plastic) in 24 defined areas each. Windows and tools were cleaned with Microbac forte (Hartmann) or DNA Exitus (Applichem). Subsequently, 10 consecutive rubbing movements were carried out on the tools 3 times a day on 3 consecutive days under light pressure. The prepared scrapings were analyzed in a standardized manner (DNA extraction with EZ1 DNA-Investigator Kit, Investigator Lyse/Spin-Basket Kit from Qiagen; quantification using real-time PCR, Investigator Quantiplex Pro Kit from Qiagen, multiplex PCR with PowerPlex® ESX 17 Kit from Promega and capillary electrophoresis using 3500 Genetic Analyzer from Applied Biosystems and Gene Mapper ID‑X software). During the analysis of 72 traces, DNA was detected at a concentration of 22 pg/µl on a lever trace placed on a plastic window with a screwdriver and a homogeneous DNA profile was generated.

A retrospective analysis was then carried out to empirically verify the extent to which the experimental data corresponded to actual investigative casework trace evidence. For this purpose, the 90 lifting traces examined in a 3-year period prior to the experimental study were analyzed with respect to the proportion of DNA profiles detected. A total of 9 mixed traces could be analyzed as well as a completely homogeneous profile pattern that could be assigned to a suspect based on the investigative approach. These data should be taken into account in a specific investigation when weighing up the costs and benefits of analyzing traces at the actual lever mark.