To add some perspective here, Justice Scalia went so far as to claim the government has the right to kill a known-to-be-innocent person so long as they were at some point found guilty by a habeas court.

Here's the quote:

“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.”

I personally loved Alan Dershowitz's retort, though it's a lot less relevant than the words of someone who sits on the Bench:

"Let us be clear precisely what this means. If a defendant were convicted, after a constitutionally unflawed trial, of murdering his wife, and then came to the Supreme Court with his very much alive wife at his side, and sought a new trial based on newly discovered evidence (namely that his wife was alive), these two justices would tell him, in effect: “Look, your wife may be alive as a matter of fact, but as a matter of constitutional law, she’s dead, and as for you, Mr. Innocent Defendant, you’re dead, too, since there is no constitutional right not to be executed merely because you’re innocent.”"

http://www.thedailybeast.com/articles/2009/08/18/scalias-cat...