Biological Evidence Management for DNA Analysis in Cases of Sexual Assault

Abstract

Biological evidence with forensic interest may be found in several cases of assault, being particularly relevant if sexually related. Sexual assault cases are characterized by low rates of disclosure, reporting, prosecution, and conviction. Biological evidence is sometimes the only way to prove the occurrence of sexual contact and to identify the perpetrator. The major focus of this review is to propose practical approaches and guidelines to help health, forensic, and law enforcement professionals to deal with biological evidence for DNA analysis. Attention should be devoted to avoiding contamination, degradation, and loss of biological evidence, as well as respecting specific measures to properly handle evidence (i.e., selection, collection, packing, sealing, labeling, storage, preservation, transport, and guarantee of the chain custody). Biological evidence must be carefully managed since the relevance of any finding in Forensic Genetics is determined, in the first instance, by the integrity and quantity of the samples submitted for analysis.

Forensic Genetics and Genotyping

“…Saliva transports exfoliated epithelial cells from buccal mucosa which contains DNA and the mean number of epithelial cells per 1 mL of saliva is about 4.3 × 10 5 , which makes it a suitable source of genomic DNA (8,11,18). Some studies have shown that DNA of perpetrator may be detected in the victim's oral cavity up to 1 hour after intense or constrained kissing (8,10). Saliva can also be placed on human skin through kissing, biting, sucking and licking.…”

“…The fingernail hyponychium can provide a valuable source of evidential material for investigation (8,21). Traces of skin (especially if the victim scratched the perpetrator), body fluids and hairs may collect under the nails.…”

“…Also, the hair melanin is significant inhibitor of PCR DNA amplification, and therefore roots are preferable. Hair chemical treatments may furthermore decrease amount of DNA (8).…”

“…In order to prevent DNA degradation, a forensic examiner must correctly select the type of material used for collection and storage (e.g. paper versus plastic bags) and ensure complete drying of the sample prior to packaging (8).…”

Assessment of DNA and mtDNA Degradation in Sperm Cells Collected by Laser Micro-dissection

“…However, collecting biological samples beyond 72 hour after the occurrence greatly diminishes the chances of recovering the DNA profile from the perpetrator [4]. Sperm cells start lysing and the DNA becomes increasingly degraded, rendering an analysis impossible.…”