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.
Highlights
In violent deaths, bloodstain pattern analysis (BPA) can provide useful information about the physical events that led to bloodstains deposition, such as the nature of weapon used, the type of injury, and the approximate positions of the individuals and objects in space [1]
Considering that fly artifacts originate from a mixture of human and fly biological material and that the cytochrome c oxidase subunit I (COI) gene is the standard locus for DNA barcoding in invertebrates and for identification of forensically important fly taxa [13,14,15], this study aimed to develop a suitable molecular approach to assess the presence of fly’s COI gene in fly artifacts from human blood in order to distinguish them from genuine bloodstains
The setting up of the fly box with C. vomitoria produced on all the walls several fly artifacts of different morphology spanning from red and brownish/light brown, circular and elliptical stains to artifacts with sperm-like tail or a tearshaped body (Fig. 1)
Summary
Bloodstain pattern analysis (BPA) can provide useful information about the physical events that led to bloodstains deposition, such as the nature of weapon used, the type of injury, and the approximate positions of the individuals and objects in space [1]. Some alterations could be considered as part of the bloodstain pattern and used to recreate the death scene [2], but others can act as confounding factors. This is the case of insect stains defined as “bloodstains resulting from insect activity” by the Scientific Working Group on Bloodstain Pattern Analysis (SWGSTAIN) [3]. As blowflies feed on and digest biological fluids as blood, semen, and saliva, fly artifacts could contain sufficient amounts of human biological
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