It usually has to be overwhelming though, and with the witnesses recanting, some of them even saying the cops pushed them into their testimony, that does not sound like the case here.

The larger issues though, are that

1) Even with someone else claiming to have murdered the victim, it will NEVER be investigated now because cops and prosecutors got their man. That means that if both he and the executed man are telling the truth a murderer will remain unhindered and unsuspected amid society until he commits ANOTHER such crime and

2) Even if overwhelming, incontrovertible proof comes to light that Davis was innocent and someone else guilty comes, this can never be undone. There is no way to compensate him for the loss of his life or his family for the loss of their loved one and

3) If he can be executed on the basis of such dubious evidence, anyone can, raising the question of whether the death penalty can be much of a "deterrent" when people can easily be subjected to it whether they commit any crime or not. Even the most serious penalty deters no one from anything when they face it whatever they do, and a lot of folks will just figure "if you must do the time, you might as well do the crime."

I am a big fan of life without parole, consecutive sentences etc. That Sirhan Sirhan and Manson are eligibly for parole, even if they will never get it, is a travesty and frankly disturbing, and I do NOT like knowing that it is largely up to the shrinks whether Anders Breivik will be on the street before he turns 50. I am also dubious of releasing someone early for "good behavior" when they were only there because they first behaved BADLY enough to shoot up Burger King over a sandwich with onions. None of that makes something as irrevocable as capital punishment a good idea, especially when it is so often imposed in such questionable circumstances. I am also appalled by prematurely foreclosing the opportunity for repentance and salvation that I consider so priceless; I recognize that many people do not find that compelling, but would not want to answer for it personally. I hope GA got the right man, but God only knows; anyone else is only guessing.