NCJ Number
248188
Journal
Journal of Forensic Identification Volume: 64 Issue: 5 Dated: September/October 2014 Pages: 429-448
Date Published
October 2014
Length
20 pages
Annotation
This study compared traditional biological collection methods for DNA recovery with a wet-vacuum system in the collection of different volumes of blood on tile, denim, and carpet.
Abstract
The study found that the wet-vacuum technique recovered sufficient amounts of blood for Kastle-Meyer presumptive testing. Although it was possible to detect blood after wet-vacuum collection, swabbing resulted in the highest rate of positive results for the presumptive test. The DNA yields and detection limits that were obtained when collecting from tile were similar between methods, suggesting they are equivalent in their ability to collect DNA from nonporous surfaces. When the techniques were tested on mock case surfaces, wet-vacuum collection resulted in higher DNA yields than either the double swab or toping methods; however, short tandem repeat (STR) profiles that were obtained from these mock surfaces exhibited extraneous alleles at many loci. This suggests that these higher yields resulted from collecting DNA already present on the substrate. In addition, the wet-vacuum collection efficacy was tested by examining yields that were obtained when semen and blood were collected from tile, denim, carpet, and brick. Results indicate that the technique can collect DNA from all surfaces, although the yield from brick varied widely and was low compared to the other substrates. Of the 16 low-volume samples collected from brick, 8 resulted in no detectable DNA. Tests that examined the wet-vacuum technique's propensity to spread samples were also performed. DNA was detected up to 4 inches from the collection site, suggesting caution should be taken when collecting biological evidence that is in the vicinity of another probative sample. 4 figures, 5 tables, and 14 references