In criminal trials, juries and the public in general tend to put a lot of weight on science when deciding whether a criminal defendant is guilty of a charge. The slam dunk of evidence, at least as it is often seen in movies and on TV, is when DNA evidence connects a defendant to the scene of a crime.
A current DNA controversy in an out-of-state medical examiner's office, however, shows that science isn't perfect. Why? Because it is subject to human error, for one thing. In 2011, a technician at a medical examiner's office left her job after the quality of her work came into question. She worked with rape kits in order to collect DNA evidence that would work to incriminate or exonerate suspects.
Working with sex crime evidence likely is filled with pressure, but the gravity of the situation should lead to extreme meticulousness and accuracy in a technician, not sloppiness. More than 800 New York rape cases must be reviewed because of possible mishandling of evidence. The review has already discovered evidence that identifies possible rape suspects, evidence that may have helped take the blame off of innocent targets.
Sources claim that no one was wrongly convicted of a sex crime because of the particular lab technician, though that is just a claim and not a hard-and-true fact. That claim seems less credible, too, since The New York Times reports that the former technician was guilty of the cross-contamination of samples. That means that evidence from different cases got jumbled up during an investigation.
This one person in a science lab is responsible for researchers having to address several hundred rape cases. Imagine the scope of cases that could be compromised on a larger scale if more technicians are even just half as irresponsible as this one worker reportedly was.
Source: The New York Times, "New York Examines Over 800 Rape Cases for Possible Mishandling of Evidence," Joseph Goldstein, Jan. 10, 2013