Collecting Touch DNA Evidence
Touch DNA exists where a perpetrator has touched a surface at the crime scene, possibly leaving a fingerprint as well as DNA. Having the proper supplies on the scene, and the knowledge to use them, is critical to the collection of usable DNA samples. A crime scene investigator’s toolkit should include basic and necessary supplies to recover DNA evidence from crime scenes.The supplies that are normally used for processing and recovering DNA samples include sterile cotton-tipped applicators (swabs) on which to collect samples, sterile water or a phosphate saline solution to moisten the swab prior to collection, and plastic pipettes to transfer the sterile water to the swab. Proper swabbing techniques for touch DNA are described in Figure 1. Helpful processes for swabbing biological materials are detailed in Figure 2. In addition to swabbing, samples may be cut from items or scraped from surfaces. Conferring with laboratory personnel may help to establish which collection method is preferred for a particular type of evidence.
From: Property Crime Sample Processing: Law Enforcement Experiences and Crime Laboratory Efficiencies by Lisa Calandro, Lynne Burley, Detective Joseph Blozis, and Lisa Schade, BS, MHR