The washing away of evidence: The effect of different washing treatments on body fluid identification and DNA profiling from stained clothing fabrics

Body fluids like blood, saliva, and semen are commonly found during investigations of crimes like homicides and sexual assaults. The identification of the biological fluid is valuable for the investigation of criminal cases to identify the perpetrator, being often decisive for the court's decision. Aware of the latter, suspects often clean their bodies and clothes after committing a crime to alter the evidence or avoid its detection. Little is known about the extent of serological testing of clothing fabric samples stained with body fluids after they have been washed. Most efforts regarding the identification of body fluids from washed clothes have been directed mostly towards the use of alternative light techniques and/or chemical assays, on the assumption that washing destroys or reduces to undetectable levels the concentration of components that serological samples use as an indicator to confirm the identity of a fluid. From another part, even though it has been demonstrated previously that DNA can be recovered from clothing laundered after the deposition of some body fluids, cleaned items are not routinely analyzed for DNA profiling. Herein, the present work shows the evaluation of the effect of four different washing treatments on 1) body fluid identification using immunochromatographic tests; 2) the yield of human DNA extraction; and 3) the integrity of the generated genetic profiles; on three types of body fluids, two volumes, and three common types of fabric. Our results demonstrate that machine–laundering cotton, denim, and polyester, even if no detergent is used, reduces the concentration of the major components from blood, saliva, and semen making difficult the identification of the protein related to the body fluids identification by using immunochromatographic tests when fluids volume is lower than 50 μL. Importantly, for small volumes of body fluid used in this evaluation it was possible to isolate human DNA from blood–, saliva– and semen–stained cotton and denim fabric with quality and quantity good enough to obtain partial and even full STR profiles. Both washed and unwashed samples showed no correlation between LFI band intensity results and human DNA concentration. Our results suggest that body fluid identification and genetic profiling can still be performed after clothes with small stains are washed and discusses a protocol that is applicable to real-case scenarios by considering body fluids volumes, and washing treatments that simulate what would be found in common crime cases.