DNA cannot prove innocenceIt can certainly prove "Not Guilty", if you don't prefer to use the term "innocent". It's the same to me either way.
Consider the obvious body fluids left by a rapist. The DNA can be so strikingly different that it excludes the majority of the global population, including a given suspect. That is exculpatory in the extreme, isn't it?
Or blond hair determined to have been left by the suspect. That belongs to certain genetic markers that can't be fooled by hair dye. If the guy being questioned has red hair, doesn't DNA from both sets of hair follicles prove inmocence, or "not guilty" if you prefer?
Like I said, it proves the person who left it was there, it does not prove that no one else was there.