A DNA-based method for distinction of fly artifacts from human bloodstains

Abstract

Fly artifacts resulting from insect activity could act as confounding factors on a crime scene and interfere with bloodstain pattern analysis interpretation. Several techniques have been proposed to distinguish fly artifacts from human bloodstains based on morphological approach and immunological assay, but a DNA-based method has not been developed so far. Even if in forensic genetic investigations the detection of human DNA is generally the primary goal, fly artifacts can provide useful information on the dynamics of crime events. The present study provides a molecular method to detect fly DNA from artifacts deposited by Calliphora vomitoria after feeding on human blood through the analysis of the mitochondrial cytochrome oxidase gene subunit I (COI). Fly artifacts originated from digestive process and of different morphology spanning from red and brownish/light brown, circular and elliptical stains to artifacts with sperm-like tail or a tear-shaped body were collected. The COI amplification was successfully obtained in 94% of fly artifact samples. The method showed high sensitivity and reproducibility, and no human DNA contamination was observed, offering specificity for use in confirmatory test. This molecular approach permits the distinction of fly artifacts from genuine bloodstains and the identification of fly’s species through the COI region sequencing by protocols usually applied in forensic genetic laboratories.

The use of fly artifacts in a crime scene: Is there any application for forensic toxicology?

“…Toxicological data provided by the analysis of dark and light FA were kept separated and compared. Morphological aspects were not taken into consideration for this study [13][14][15].…”

“…The purpose of this study is to understand if FA trace evidence permits toxicological analysis when traditional matrices are not available. To this aim, an ad-hoc crime scene was ideated and created on the base of authors' experience [13][14][15] and Calliphora vomitoria specimen were then artificially introduced for 2 days. FA were then carefully collected from absorptive and non-absorptive surfaces and analyzed for drugs of abuse.…”