As far as I can tell, this isn't actually true: "the DNA evidence that was not destroyed by the state is exculpatory". The Innocence Project are being very careful with their wording here. Initially, they relied on trace DNA on the knife that didn't match the accused murderer, but that ended up being from someone in the prosecutor's office handling it after it had been processed for forensic evidence. Then they tried to argue that this showed the state had destroyed evidence which would've proved his innocence, but the courts didn't buy it because all available evidence suggests the killer's DNA was simply never on the knife. (Which isn't that surprising - DNA evidence isn't perfect and gloves exist.) The other "forensic crime scene evidence" seems to be hothingburgers like a few non-matching hairs in a house that'd had a large number of people going in and out in the recent past.