The comparison of excision, swabbing, tape-lifting, and scraping as techniques for DNA evidence recovery: A preliminary study

In the Final Report of the Commission of Inquiry into Forensic DNA Testing in Queensland , Recommendation 28 recommended that alternative procedures to the scraping method should be investigated for the recovery of biological material from crime scene exhibits for downstream DNA testing. This study forms the first phase of a larger project comparing swabbing, tape-lifting, scraping and excision of biological fluids from a fabric substrate to determine the most effective recovery procedure. Calico cotton swatches were seeded with two concentrations (neat and 1:1000) of blood, semen and saliva, samples commonly encountered in forensic casework. Each sample type was collected using the four evidence recovery methods, extracted, quantified, and the 1/1000 dilution samples were short tandem repeat (STR) profiled to assess the practical limits of each method. Excision had the greatest DNA yield with a large effect size and best STR profile quality compared to all other recovery methods for blood ( p   0.95), semen ( p  < 0.0001, ŋ 2  = 0.96) and saliva ( p  < 0.0001, ŋ 2  = 0.82). There were no statistical differences found between the MWE Sterile Tubed Dryswab™ Rayon swab 1028, the Puritan® 6” Standard Rayon Swab w/Polystyrene Handle – 806-PR, HazPak tape-lift or scraping for neat blood and semen. Tape-lifting had a statistically higher efficiency than scraping ( p  = 0.0012), the Puritan ( p  = 0.0046) and the MWE swabs ( p  = 0.0145). Results suggest that excision is the most effective biological material recovery technique for blood, semen, and saliva from 100 % white cotton.