Scientists were able to fabricate DNA evidence which could be used in the future to question the reliability and value of said evidence. DNA evidence was not as conclusive as many people thought before this either. Lack of an exact time stamp, and the possibility that it was planted are legitimate attacks. This adds another avenue of attack.
http://www.nytimes.com/2009/08/18/science/18dna.html (via http://pajamasmedia.com/instapundit/83671)
"The scientists fabricated blood and saliva samples containing DNA from a person other than the donor of the blood and saliva. They also showed that if they had access to a DNA profile in a database, they could construct a sample of DNA to match that profile without obtaining any tissue from that person.
“You can just engineer a crime scene,” said Dan Frumkin ... “Any biology undergraduate could perform this.”"