Many items of evidence contain invisible traces of DNA even if no obvious biological staining is present. Because DNA testing has become so sensitive, items such as knife handles and firearms can be swabbed to recover invisible cellular material potentially left by handlers of those items. Due to the expected low-level DNA yield, the crime laboratory will typically swab the entire surface of the item, removing most if not all of the low-level DNA that was present. The entire swabbing is then consumed in the analysis, leaving nothing for an independent analysis.
If this so-called consumptive DNA testing is going to be performed, crime laboratories typically must first inform the detective or prosecutor handling the case.
The defense may request to have an expert present on their behalf to witness the DNA testing, since a re-test is not possible.
Mehul B. Anjaria can travel to DNA laboratories to witness consumptive forensic DNA testing on your behalf.