Precision touch DNA sampling on plastic bag knots for improved profiling of packer and holder contributions.

In forensic DNA analysis, evidence sampling stands as a pivotal step setting the ground for the quality of the forensic profiling. The collection of touch DNA from objects, when guidelines are scarce or absent, is usually governed by ad hoc decisions based on the available case circumstances. In our laboratory, in the context of illicit drug-related crimes, similar objects are frequently encountered, offering an opportunity for the standardization of evidence treatment. This study aims to develop an effective method for sampling touch DNA from knots on plastic bags. We examine both the exposed and hidden areas of knots, considering the latter as "protected" zones less likely to accumulate biological material during subsequent handling. The study contrasts a single sample method (whole knot surface sampling, Method 1) with dual-sample methods that separate exterior (exposed) and interior (hidden) surfaces of the knot. Notably, our study consistently reveals higher DNA yields from exterior surfaces of the knots as opposed to interior samples. Importantly, our findings demonstrate that utilizing a single sample may produce DNA profiles that are not interpretable, while employing a dual-sample approach may allow for the differentiation between the genetic contributions of the person who tied the knot, the packer, from the person who held the package, the holder. We have refined the dual-sample method to reduce holder DNA in the interior sample while maintaining it on the exterior, also allowing the packer's DNA to be detected on both surfaces. We explore four dual-sample collection methods. Method 2 involves taking the first sample from the exterior and the second from the interior of an untied knot. Method 3 visually differentiates between the original exposed and hidden surfaces for precise sampling. Method 4 employs tools to open the knot for interior sampling. Method 5 uses Diamond dye to highlight cell-free DNA on both surfaces before sampling. In conclusion, this study not only clarifies the complex dynamics of touch DNA transfer and collection on plastic bag knots, but also offers insights into standardizing evidence collection in similar cases.

Allele frequencies and forensic parameters of 22 autosomal STR loci in a population of 983 individuals from Serbia and comparison with 24 other populations.

BACKGROUND: Analysis of allele frequencies of short tandem repeat (STR) loci in ethnically diverse populations is essential for forensic reference database construction and studies on population genetics. AIM: To analyse genetic polymorphisms of 22 autosomal STR loci in the Serbian population and to compare them with previously published data from some European and Turkish populations. SUBJECTS AND METHODS: The study was conducted among 983 unrelated individuals from Serbia. Genotyping was performed using the PowerPlex® Fusion amplification kit. Allele frequencies and forensic parameters were calculated using FORSTAT software. Interpopulation comparisons and genetic distance calculations were performed in Arlequin and POPTREEW software. RESULTS: A total of 280 alleles were detected with corresponding allelic frequencies ranging from 0.0005 to 0.5255. Based on heterozygosity and the polymorphism information content, D1S1656 and Penta E may be considered as the most informative markers. Both the combined power of discrimination (CPD) and the combined power of exclusion (CPE) for the 22 analysed loci were higher than 0.999999. The combined match probability (CPM) for all 22 loci was 6.773688e-29. CONCLUSION: With respect to the results, the 22 STR loci are highly polymorphic and discriminating in the Serbian population and could be used for forensic practice and population genetics studies.

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

DNA analysts in forensic laboratories are engaged in analysing and sampling bloodstains from bloodstained items. Detailed and precise descriptions of bloodstains on items of interest are very important for bloodstain pattern analysis (BPA). DNA and BPA reports were examined from forensic laboratories in Serbia (N = 88). About 400 reports were observed from the past three years. First, we analysed descriptions of items (clothing and shoes) in DNA reports, and special attention was paid to descriptions of bloodstains. Subsequently, we estimated the value of descriptions of bloodstained items of interest in linking specific types of bloodstains to the obtained DNA profiles. Observed descriptions of bloodstained items in DNA reports are usually limited to phrases. A major problem exists in cases where several people were injured in the same bloodshed event. Connecting specific types of bloodstains to obtained DNA profiles is essential for the reconstruction of crime events. The complete analysis should therefore include detailed descriptions of all types of observed and sampled bloodstains. In DNA laboratories that are within a larger institute, it would be more appropriate and productive if BPA and DNA experts examined 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 the basic principles of BPA.