Tools of the Trade: Dealing with Unusual Surfaces
This article was originally published in the August, 2013 edition of Forensic Magazine.. By Dick Warrington.
For the past several years, I’ve taught a class on developing and lifting prints off unusual surfaces. This class is very popular because it shows Crime Scene Officers that the only “surfaces” where you can’t get prints are air and water; everything else can be processed with the right products and the right technique. In this issue, I’ll provide an overview of advanced ways to deal with unusual surfaces.
Some of the most challenging surfaces to work with are multi-textured or multi-contoured. If you find evidence on one of these surfaces, you need to be prepared. Otherwise, you may have to settle for simply photographing the evidence instead of casting impressions and lifting latent prints. Let’s take a look at a the products and techniques that you can use on these kinds of surfaces.
Tool marks, bite marks, other kinds of impression marks, and latent fingerprints are often found on multi-textured or multi-contoured surfaces. The AccuTrans system, which uses polyvinylsiloxane (PVS), is ideal for this type of evidence because it is easy to use, provides great detail, and sets relatively quickly. You’re also likely to get better results because the system mixes the chemicals for you. AccuTrans works like a caulking gun. Simply insert a double cartridge, add the special mixing tube, then squeeze the trigger. The mixing tip combines the catalyst and the hardener, so the PVS is properly mixed when it comes out. Apply the PVS directly to the area you want to cast, then use the tip to stir the compound to remove any air bubbles. If applying over a latent print, be careful not to allow the tip to touch the print directly, or you could ruin the print. The AccuTrans PVS comes in different colors. White is used primarily for dusted fingerprints, while brown is for tool and bite marks and gun barrels. The clear version offers an advantage for lifting prints with black powder because the lifted prints can be added directly into AFIS without needing to be reversed.
Additional information from this article can be found on www.forensicmag.com.