Because touch DNA deposited on a surface is not visible to the eye, it is difficult to link these samples
to a crime scene with the same confidence as one might a DNA sample isolated from a visible blood stain.
In order to evaluate the quality of touch DNA evidence, it is therefore critically important to understand the
different factors affecting how a DNA sample could have arrived at a particular crime scene. These factors
include (1) the background levels of human DNA in the environment, (2) the dynamics by which DNA may
be transferred to a surface by touch or other relevant activities, and (3) the persistence of DNA samples
under different environmental conditions.
