Scalia: No constitutional problems executing an innocent man

“This Court has never held that the Constitution forbids the execution of a convicted defendant who has had a full and fair trial but is later able to convince a habeas court that he is ‘actually’ innocent. Quite to the contrary, we have repeatedly left that question unresolved, while expressing considerable doubt that any claim based on alleged ‘actual innocence’ is constitutionally cognizable.” --Antonin Scalia

This is the case he's talking about. Seven of 9 eyewitnesses have now recanted.