See New Scientist for an article called "Fallible DNA evidence can mean prison or freedom" by Linda Geddes, dated 11 August 2010.
Interpretation of DNA analysis can be subjective and it is vulnerable to suggestion, so that scientists should know nothing of the circumstances in which samples were obtained or about the prosecution theory of the case.
The article points out that a defendant could be wrongly convicted because an analyst says that samples matched, when in fact peer opinions may differ over that and indeed may favour the contrary conclusion.
I suppose some defendants might wrongly be acquitted if an analyst thought there was no match, when peers might think there was a match. Could that happen?