Identification Of Bloodstains

The value of blood evidence in the investigation of crimes is widely appreciated. Bloodstains have the potential to provide a multiplicity of information, most notably through DNA fingerprinting and bloodstain pattern analysis. It is vital that forensic practitioners are able to identify bloodstains upon any surface, by following justifiable scientific principles and procedures that ensure such evidence is admissible in court.

Despite the recognised value of blood evidence, there is a dearth of academic knowledge regarding environmentally altered stains - specifically, the ability of presumptive tests to identify bloodstains on fabrics that have been machine-washed at a range of temperatures, as may be encountered with clothing from a crime scene. Therefore this paper investigates the efficacy of sight, UV, Hemastix, and BlueStar luminol tests for detecting latent bloodstains on denim, cotton, and acrylic fabrics following machine-washing at 30°C, 40°C, 60°C, and 90°C. All washes (N=60) included active oxygen, a product that has been identified as effectively concealing bloodstains from presumptive tests.

This study found bloodstains washed at 30°C were detected significantly more frequently than those washed at 60°C or 90°C. The Hemastix test results were consistently positive, but washing acrylic at 60°C or 90°C provoked a false-negative BlueStar result. Remarkably, it was noted that washing acrylic at any temperature using active oxygen resulted in a false-positive BlueStar chemiluminescent reaction, a phenomenon that has never previously been reported.

In light of these results, this study recommends that practitioners use Hemastix as their primary presumptive test for blood trace evidence on washed clothing; whilst the use of luminol remains valuable for revealing bloodstain morphology, the potential for false-negatives and false-positives means the chemiluminescent results must be interpreted intelligently. These recommendations can aid forensic practitioners in the analysis and submission of washed clothing, improving prioritisation and thereby saving both time and money.