If you believe or maintain that DNA evidence is “infallible” or beyond question I strongly recommend that you obtain a copy of the April, 2006 issue of Discover magazine and read “WHO'S YOUR DADDY? Don't count on DNA testing to tell you” (Pages 68-69).
The considerable and serious questions raised therein, as to DNA testing, are based on the following two problematic areas: Inaccurate (ie “Sloppy”) testing of the provided samples; And, the phenomena of persons (Called Chimeras) who DNA “signatures” vary according to the place from which samples are taken.
As to lab errors, you should recall the not too-long-ago flurry of news as to errors in medical testing due to errors committed by overworked technicians. It appears from the noted article that the same can be the case in paternity cases and, perhaps, in criminal cases. Defense attorneys and their opponents, should insure that DNA samples are: Kept in a legally AND scientifically secure manner; Divided up and randomly selected for testing so as to maintain a fair sample for independent testing if the defense requests it; And, used as evidence if-and-only-if the reliability of the testing agency and technician can be demonstrated. To do otherwise would leave the prosecuting/plaintiff's case open to serious challenges and doubts—In the trial court or upon appeal.
On the other hand, there may be cases where the innocence of convicted criminals was “proved” by DNA evidence may be in error IF the post-conviction sample were from (As is usual) a mouth swab and the original material was blood, semen, fingernail scrapings (Presumed to be from an attacker) or the like AND the accused is a chimera. To assure the validity of DNA testing in such cases, the source of tested materials should be the same in pre-conviction and post-conviction testing OR evidence presented that the accused is NOT a chimera.
I suggest that you keep the above in mind when reviewing news stories based on DNA testing.