Topic: Primer residue testing and trace metal detection on hands

[MEG]

Our crime scene unit is routinely called to stub hands for primer residue in a variety of cases. I would like to get some feedback on the pros and cons of continuing to do so given issues such as contamination and interpretation of results.
Also, any feedback on trace metal tests would be appreciated. I am referring to those color development sprays which are applied to hands.

Much Thanks,

Mike

[Bob Shem]

Here's the way I see it.  Scientific testing is conducted to answer questions that come up in the course of a criminal investigation.  One question that routinely comes up in a shooting event is "Who pulled the trigger?"  Primer residue testing cannot answer that question.  Primer residue testing can answer the question "Is there primer residue present?"

Let's assume that the answer to the second question is "Yes".  What does that mean?  All it means is that someone's hands are contaminated.  It tells us nothing about how the residue got there.  The residue could have come from handling a "dirty" gun.  It could have come from handling something within the residue cloud after a discharge.  It could have come from having hands in close proximity to the discharge.  It could have come from shooting a gun.  It could have come from an officer who handcuffed the suspect after holstering his weapon.

The vagueness of the interpretation of the data and the inability of the test to answer the question "Who pulled the trigger?" is the catalyst for our lab to routinely suggest to agencies to avoid the test unless the question they are attempting to answer is "Is there residue present?"

[Jim Campbell]

Ditto what Mr. Shem said.

Additionally, if the test is negative does that mean that the person tested did NOT recently fire a weapon?  The answer to that is, he may have.  So does this negative unfairly help the prosecution or the defense?