DNA Analysis and Document Examination: The Impact of Each Technique on Respective Analyses

Abstract

Threatening letters, counterfeit documents, and anonymous notes can commonly be encountered in criminal situations. Such handwritten documents may encourage DNA to transfer from the writer's hands and lower arms when these areas come into contact with the document. As any DNA transferred is likely to be at a low level, sensitive low copy number (LCN) DNA analysis can be employed for testing document exhibits. In this study, we determine locations on the document that are most commonly touched during writing and handling and compare DNA recovery from these sites. We describe the impact of DNA sampling on subsequent document examination techniques including the ESDA(®) and likewise the effect of the ESDA(®) and two other document examination techniques on subsequent DNA analysis. The findings from this study suggest that DNA results can be obtained through targeted sampling of document evidence, but that care is required when ordering these examination strategies.

Non‐destructive DNA recovery from handwritten documents using a dry vacuum technique

“…Reversing the process and swabbing the documents after ESDA treatment resulted in reduced DNA amounts [13]. The latter can be explained by a transfer of the DNA containing biological material to the ESDA foil [9].…”

“…The proposed dry vacuuming swabbing method for handwritten documents does not negatively affect latent fingermark and questioned document evidence, which means this method could enable a laboratory to recover critical DNA evidence as the first step in the evidence examination workflow. This would eliminate the loss of DNA reported for fingermark development processing using, for example, ninhydrin and the contamination risk associated with frequent handling of an item and shared equipment such as scanners, ESDA apparatus, or development chambers [2,3,13,29,30]. The new workflow could start in a DNA‐free examination room with the scientist wearing a full set of protective gear including a facemask.…”

“…That means fingermark development still needs to precede DNA collection and DNA transfer from other areas of the hand is being ignored. Targeted collection from either the margins or the fold lines, where study participants had been observed to have had contact resulted in DNA typing success rates of 25% [13]. With vacuum collection over the whole surface, 81% of the STR‐typed copy paper samples were either full AmpF l STR Identifiler profiles or mixtures with LRs supporting a positive association to the known donor.…”

“…Swabbing techniques like dry swabbing or wet-dry swabbing are the most common methods used to collect potential touch DNA on a variety of surfaces. For paper, non-targeted swabbing on a surface area without prior fingermark detection will cause smudging of potentially valuable fingermarks [12,13].…”

“…Logically, the writer of the note would slide their hand and lower forearm across the paper surface and possibly smudge latent fingermarks during the writing process, while leaving better quality fingermarks on the margins of the document. It has been noted that research participants contacted the margins up to 65% of the time while writing [13]. In an analysis of DNA transfer by different regions of the hand, McColl et al reported that the hypothenar region, which runs along the pinkie finger side of the palm, deposited the greatest overall quantity of DNA on glass substrates [14].…”