DNA plays a huge role in the modern court system when determining guilt or innocence. It also may be used in appeals or when cracking “cold cases” that investigators could not solve in the past.
Experts sometimes refer to “trace” DNA as “touch” DNA. According to Nature, trace DNA is DNA that a forensic expert obtains from shed skin cells or other biological matter that transfers from a donor to an object or another person via physical contact.
How do forensic experts gather trace DNA?
The recovery of DNA from surfaces is subject to all manner of unmanageable factors. For instance, the type of contact between the shedder and alleged offender as well as environmental conditions both at the time of contact and after can significantly alter the means of DNA recovery.
Gathering trace DNA requires targeting a relevant area of wherever the expert is trying to collect the DNA from. However, there are multiple problems with common methods of gathering trace DNA. For instance, the “cutting out” method, which involves cutting out pieces of a garment so that experts can test them for DNA, does not conserve the garment. This can be problematic for evidential reasons. Additionally, both inner and outer surfaces of a garment must be tested at the same time using this method, which can produce uninterpretable mixtures.
How does trace DNA affect the courtroom and appeals?
Trace DNA has had a strong impact on appeals and convictions: for example, trace DNA helped clear JonBenet Ramsey’s family of suspicion in 2008. The defense also used trace DNA testing on duct tape on the remains of Caylee Anthony in the defense of Casey Anthony, as Casey’s DNA was not found on the duct tape.