I haven’t researched this case, but those who oppose the death penalty push the notion that without DNA evidence, no conviction is legitimate. It is false that DNA will always be present, and that testing whatever was found will be definitive. Making it impossible to convict the guilty fails the cause of Justice just as much as framing the innocent.
Did the jury convict this guy on zero evidence? No fingerprints, none of the victim’s blood, hair, etc. on the murderer or his clothes, no murder weapon connected to the killer, no surveillance video, no witnesses, nothing to place him at the scene, solid alibi, nothing stolen from the scene found in his possession, no recorded conversations/confessions, no history of robberies and violence, no means motive or opportunity, etc.? I would think the 20+ years of appeals would have mentioned flaws in the total case rather than latch onto the unknown.