DNA means nothing?
http://www.news-press.com/story/news/2016/09/28/cape-coral-police-make-arrest-cold-case/91212964/
Like all other evidence, DNA evidence has a context and chain of possession.
If my wife turns up dead and they find my DNA on her body, does that prove I killed her? Nope. Proves nothing. We sleep in the same bed, sit on the same furniture, drive the same cars, and have done so for over 30 years.
If they find a stranger's DNA on her clothing does it prove anything? Nope. Every stranger she comes in contact with today, all of her coworkers, and the people who inspect, manufacture, and sell her clothing all can leave DNA on her clothes.
DNA Evidence, like all other evidence, only means something when it proven too be admissible, and even then only under the circumstances appropriate to its admission.