Recovery of total dsDNA from bloodstained painted brick surfaces after hydrogen peroxide cleaning and repainting

Background Suspects often attempt to conceal biological evidence at crime scenes through chemical cleaning and repainting, making forensic DNA recovery challenging. Hydrogen peroxide (3%) is a commonly used cleaning agent, and repainting may be used to conceal visible bloodstains. This study investigated the recovery of measurable total double-stranded DNA (dsDNA) from bloodstained wall surfaces following hydrogen peroxide treatment and subsequent repainting with white satin paint. Results Blood samples obtained from 10 healthy volunteers were applied to 30 UV-treated plastered brick surfaces coated with satin paint and assigned to three groups: untreated (reference), hydrogen peroxide-cleaned, and hydrogen peroxide-cleaned plus repainted. Following luminol visualization, DNA was extracted from scraped surface samples using the QIAamp ® DNA Investigator Kit and quantified with a Qubit™ 4.0 Fluorometer. The reference group produced the highest mean total dsDNA concentration (5.043 ± 3.110 ng/µL), whereas the hydrogen peroxide-cleaned and hydrogen peroxide-cleaned plus repainted groups yielded lower mean total dsDNA concentrations of 0.361 ± 0.166 ng/µL and 0.342 ± 0.074 ng/µL, respectively. A significant overall difference was observed among the three related conditions (Friedman test, χ²(2) = 15.00, p < 0.001; Kendall’s W = 0.75). Pairwise Wilcoxon signed-rank tests showed significant reductions in total dsDNA concentration after hydrogen peroxide cleaning and after hydrogen peroxide cleaning followed by repainting compared with the untreated condition (raw two-sided p = 0.00195 for both comparisons; Bonferroni-adjusted α = 0.0167), whereas no significant additional reduction was observed after repainting compared with cleaning alone (raw two-sided p = 0.941). Conclusion Although hydrogen peroxide cleaning and repainting substantially reduced the measured total dsDNA concentration, measurable total dsDNA remained detectable in all tested samples. These findings demonstrate that total dsDNA can remain recoverable from blood-treated wall surfaces after cleaning and repainting under the controlled experimental conditions evaluated.