Criminology

From a forensic or investigative perspective, it is preferable to seize different types of trace evidence in the first instance because it can provide a broader investigatory framework, because it can answer more questions than DNA evidence alone, and because DNA evidence is effectively a derivative of certain types of trace evidence.

First, trace evidence can provide an investigatory framework whereas DNA evidence is mainly used for purposes of confirmation.  Trace evidence, for example, can be used to establish or otherwise reconstruct how a crime or other event happened.  It therefore functions as a tool of construction from which theories and other clues may be pursued and tested.  It is true that DNA evidence may be used as part of a DNA profile this type of process, however is much narrower in scope and application than what can be accomplished through the seizure of trace evidence.

Second, forensic examiners and investigators can answer more questions through the seizure of trace evidence than they can with DNA evidence.  To be sure, a DNA sample without more may very well be such a slim seizure of evidence that investigators are never able to link it to the crime because of a lack of supporting evidence upon which to reconstruct events.  It is true that some trace evidence is not admissible in courts of law as independent pieces of evidence, and that it sometimes offered as a type of corroborating rather than direct proof, but that does not diminish its significance in the building the case so that it may reach a court of law in the first place.  

Finally, DNA evidence is essentially a derivative of trace evidence more particularly, it is through the collection of certain types of trace evidence that DNA may be seized.  The confirmation function performed by DNA evidence is therefore dependent on some underlying trace evidence.  In the final analysis, it is far wiser and more preferable to seize and properly preserve as much trace evidence as possible.