Detectability, visualization, and DNA analysis of bloodstains after repainting the walls.

A recurrent observation in forensic casework is that culprits and/or their abettors attempt to remove or mask bloodstain patterns, e.g., by painting the walls. The present study was designed to elucidate whether luminol treatment of bloodstains on (a) plastered and (b) wallpapered walls may help with the visualization of respective patterns after being repainted beyond macroscopic recognition. Furthermore, wallpaper punches of luminol-positive spots were analyzed for DNA. The experiments showed that the prospects for visualization after a four- to sixfold paint application declined considerably as the drying time of the paint increased. A compelling explanation for this observation is that paint becomes increasingly resistant to water during the drying process after paint application. In these cases, moistening the surface in question with distilled water for 15 min has been proven to be a promising pretreatment before luminol application. DNA analysis revealed full STR profiles in 74% of luminol-positive wallpaper punches, whereas rubs of the aforementioned positively tested regions (luminol and human blood pretests) demonstrated negative results.