depends what definition of innocent you seek?how many Americans are killed that are later found to have been innocent?
sugggar
the dna exculpatory version
post-trial post-execution exculpatory ambiguity re: conflicting evidence brought to light
post-execution evidence of perjury by key witness
and other categories...
no doubt there have been dozens of examples in each category. But one definition of justice, is seeing the temporal trial played out with due respect to the trial process, and the appeals play out. Regardless if the verdict was incorrect, as long as the process prevails, one definition of justice will see justice being seen to be done.
on this last hypothetical, there have been significant numbers of executions that have gone forward, where strong conflicting evidence was tainting the factuality of the trial verdict, and subsequent execution. evidence come out in months/weeks prior to execution.