As mentioned back here, there is plenty of evidence that Cameron Todd Willingham, who was executed in Texas in 2001 for (they said) starting a house fire that killed his three children, was innocent. As I said then and have said elsewhere here, it's tough to prove conclusively that a wrongful execution occurs. Once the state kills a guy, they do everything they can to make sure no one can prove the guy was innocent.
Now, Governor Rick Perry — on whose watch Willingham was terminated — seems to be doing everything he can to make sure no one proves the guy was innocent. Barry Scheck, co-director of the New York-based Innocence Project and man I'd really respect if he hadn't worked for O.J., compared the move to Nixon's infamous Saturday Night Massacre. One hopes Perry's move will be just as effective as Nixon's was.