"Innocent" is an interesting word.
1) Despite all the hoopla, AFAIK nobody has definitively proved anyone has been executed in America for a crime he didn't commit.
2) A very large percentage of those released as "innocent" due to new evidence, usually DNA, are not innocent in any meaningful sense, they are merely innocent of the particular crime of which they were convicted. Many if not most of them are career criminals who have committed dozens or hundreds of crimes for which they were never charged, much less convicted. If one of these career criminals is occasionally convicted of a crime he didn't actually commit, I have some difficulty seeing this as anything other than a case of poetic justice, or perhaps of God having a sense of humor.
Which is not to say we shouldn't improve our criminal justice system wherever we can. I really am not in favor of punishing people for crimes they didn't commit, even if they are indeed "bad people."
But I don't think there are large numbers of "innocent people," in the sense of non-criminal types, in prison for capital murders they didn't commit.
The problem with this is that when a total scumbag is convicted for a crime they didn't commit, it means that there is another scumbag who got away with it.
Interesting bit of trivia on this point: As Governor of Texas, George W. Bush commuted the sentence of exactly one condemned man to a sentence of life in prison. The man? Notorious serial killer Henry Lee Lucas. Despite being linked to dozens, if not hundreds of murders, Lucas was convicted of a mere eleven killings and sentenced to death for only one, a yet-unidentified Jane Doe known in case files only as "Orange Socks" (the sole items of clothing her body was found wearing). In a strange twist of irony, later investigations determined that this single victim, Orange Socks, was most likely killed by someone other than Lucas. Faced with these findings, Bush really had no choice but to commute the sentence.
Lucas would die in prison of heart failure a couple of years after his commutation while the true killer of Orange Socks has yet to face justice. The important point is that had Bush not exonerated Lucas for this single murder, the case files on Orange Socks would've been closed. Crime solved. Lucas did it. At least today her file remains open and while the chances of her killer being apprehended are slim, there's still a chance that justice may eventually be served.
I missed this part of your comment when I posted my reply #50.