Roger Martz, an FBI Special Agent in the Chemistry Unit, testified over two days in July 1995 about EDTA testing of blood from the sock and rear gate, evidence involved in the dispute over whether blood had come from preserved samples. Under questioning by Robert Blasier, Martz addressed destroyed raw data, undocumented procedures, sample-quantity estimates, his combination of two sock bloodstain cuttings, and his use of a negative-ion mass-spectrometry test that was less sensitive in this instance but more specific. In examinations involving Marcia Clark, he distinguished detecting a compound from identifying it and testified that EDTA was not positively identified in the evidence stains, while reference blood produced identifiable EDTA signals.