now if a parole board frees a convict and that convict kills again should the parole board be executed? what if a judge lets a mope walk on a 'technicality" and the mope kills?
If a prosecutor knows the defendant is innocent and obtains a death sentence you might have a point. Same with a judge. But you are engaging in fantasy thinking that this happens in the vast majority of the cases. Witnesses lie or witnesses are mistaken. Juries can be wrong.