I'm agreeing with your conclusion but not with your reasoning.

You reason that since it looks like he might be innocent, he shouldn't have been executed. Extrapolating from this yields that you also believe that if you felt he was definitely guilty, he should have been executed.

I'm saying that because this uncertainty exists at all as a concept the death penalty should be abolished. Its impossible to prove someone's guilt 100% in these cases, therefore the death penalty is immoral. Not just in this case but in every case.