Persistence of Stains and DNA on Evidence in Hostile Situations

Abstract

010 Abstract In order to exploit DNA evidence, biological liquid must be detected and recovered. It has been suggested that some hostile conditions like a long water soaking period may have an influence on evidence recovery and thus results and interpretation. These researches demonstrate that adapting a protocol for each situation allows to recover any evidence. It still possible to detect and identify blood stain after a washing machine even at 90°C. For semen stain, detection is not possible due to the elimination of the acid phosphatase, but spermatozoa can persist on clothes and a DNA profile can be obtained. Contact cells can be recovered on support which has been immerged in water even several weeks or in contact with fire extinguisher powder or liquid. This study shown that if cells dry enough time to adhere to the support (>1 hour) before water immersion, it is possible to obtain a DNA profile. at 30, 60 or 90 °C programs (Table 1) with detergent. Pieces of fabric are air dried and stored at room temperature until examination. Glass slide, water immersion and cell visualization Slides are immersed in water at room temperature and air dried according to the protocol. Glass slide are colored with Nuclear Fast Red and examined under X20 magnification. Stain detection and samples collection Semen stains are tested for presence of seminal liquid by acid phosphatase using brentamine fast blue technique. Cotton fabric are cutted out and spermatozoa are observed after glass preparation and coloration with hematoxylin-eosin. Blood stains are tested for the presence of blood by peroxidase using luminol method (Bluestar, according to the manufacter recommendations) and Phenolphtalein method (Kastle Meyer KM) and collected by cut (cotton fabric). Cells are collected by using moistened swab.