Here's a document from the Southwestern Institute of Forensic Sciences in Dallas regarding an interesting finding on a proficiency test.
According to the supplier of the serology proficiency test (SERI), the test slide in question contained seminal fluid but no sperm cells. However, the lab tech said her test came back positive for both. The supervisor of forensic biology, Dr. Stacy McDonald, reran the test and claimed she, too, found a single sperm cell on the slide.
Now that raises an interesting conundrum - was the test supplier mistaken in what was on that particular slide or was the lab contaminated? Did SWIFS cover up an incorrect result on a proficiency exam? If SWIFS did cover up the test result, what was the source of the sperm cell on the test slide? If there was a contamination issue at the lab, when was it discovered? And what was done to resolve the problem? Were defense attorneys made aware of contamination issues at the lab?
According to this document, SWIFS did not implement an investigation to determine the source of the contamination. If there was no cover up, why didn't SWIFS notify SERI of the contamination of the slide in question?
CAR 06-006 FBU Proficiency Test Discrepancy
Sure, it was just a proficiency exam. But what if this had been an evidential sample in a criminal case? What if someone's life hung in the balance? How much confidence would you place in the lab?