When you get to the issue of why there have been so many exonerations, though, a couple other issues must be factored in.  Obviously, you could not have exonerations if you didn't have the wrongful convictions in the first place.  But, Dallas also uses the Southwestern Institute of Forensic Science (which is commonly referred to as the Dallas County crime lab) for all its testing and SWiFS doesn't destroy any of their evidence.  That is why they still have evidence from a case like this, where, 27 years after his conviction, all this man's appeals have been exhausted and the courts have essentially told him he can't file any more appeals.  In many jurisdictions, any evidence from such a case would have long ago been destroyed.  But, SWiFS kept everything, and so it can be tested.  The second factor is that, ever since Craig Watkins got into office, he has reversed the previous policy in Dallas--and the same policy that seems to exist in just about every other jurisdiction--to oppose every request for post-conviction DNA testing.  Instead of opposing them, he is working with the state Innocence Project to help identify cases that should be looked at again.  That is why there have been so many exonerations in such a short period of time.

My experience in Dallas pre-dated Watkins' election.  One of the attorneys in our office handled most all of the requests for post-conviction testing if the person didn't have their own retained counsel.  And the DA's office opposed those requests every time.  And many of the judges--including the appellate judges--read the law that provided for post-conviction testimony so narrowly, that people who should have gotten it as a matter of routine were denied.  I remember reading one opinion about a child rape case that baffled me.  The post-conviction testing law in Texas requires that identity have been an issue (as opposed to consent, for example) in the case in order to get testing.  This appellate court opinion upholding the trial judge's denial of the DNA testing request said that because the victim unequivocally positively identified the defendant as her assailant, identity was not an issue and he was not entitled to testing.  So, in their minds, identity wasn't an issue as long as it wasn't an issue for the victim.