It's not entirely that simple. Let me try and explain the facts, i don't necessarily agree the jury's interpretation.
Cox was accused of rape in a criminal matter. An investigation was conducted including which included a paternity test. The Defense could have sought to exclude the paternity test. If they did, they were unsuccessful. The paternity test was admitted into evidence. The defense doesn't want a new test because it would likely come back positive and show some form of sexual contact between Cox and the victim. The prosecution wouldn't want a new test because the results favored their case. Rather than move to exclude the evidence, the defense chose to convince the jury that the collection process was improper. The jury was still allowed to hear the evidence and still chose to acquit. Cox's own attorney admitted that his client was a liar (i believe in reference to sexual contact with the accuser), but the DNA, if reliable, could only prove sexual contact occurred. It couldn't prove a rape had occurred. It's not the job of the defense to explain all the facts of the case, only to show that the prosecution's allegations could not be proved beyond a reasonable doubt.
The defense was able to paint the accuser as sexually promiscuous based on testimony from Demaryous Thomas that the accuser had performed sexual acts with another woman willingly before leaving the apartment the same night. (
http://www.denverpost.com/broncos/ci_20097030)
The Jury initially chose not to discuss the case. The foreman later changed his mind:
http://www.google.com/url?sa=t&rct=j&q= ... 2450,d.cGE
Again. By no means am i trying to justify the actions of Cox. I'm only trying to explain the rational for an acquittal.