Whether or not the DNA proves them innocent, it's pretty clear prosecutors withheld exculpatory evidence. When the DA gave attorneys with the Innocence Project of Texas and the national Innocence Project their case file:
attorneys found letters from the inmates who had testified that they’d heard the two men admitting the murder.The Michael Morton Act passed in 2013 required prosecutors to make such evidence available to the defense before trial, but clearly to deal with older cases there should probably be some sort of post-conviction discovery available in habeas proceedings. If Dallas DA Craig Watkins' office hadn't voluntarily opened up its files in this case, the underlying prosecutorial misconduct would never have been discovered.
During their court testimony, the informants said they had not been “promised, sought or expected any personal benefit for their testimony.”
But letters from those inmates found in the file demanded benefits, such as reduced sentences for pending charges, that they “believed they had been promised from the state in direct exchange for testifying.”
“The prosecution not only failed to turn over this material,” the brief said, but concealed it while “insisting” to jurors “that no such discussions with these informants had ever occurred.”
The two jail informants have now told the defense attorneys their testimony was false, the filing says.
It's also worth mentioning that the original case relied heavily on jailhouse informants, but if the case were retried today that testimony would have to be corroborated. Texas law didn't include such a requirement until 2009 when state Sen. Juan "Chuy" Hinojosa passed a corroboration mandate for jailhouse snitch testimony.