Why do you insist on such guarantees when you cannot guarantee that only the guilty will be executed?
Here's my trite quotation:Sir John Fortescue's De Laudibus Legum Angliae (c. 1470) states that "one would much rather that twenty guilty persons should escape the punishment of death, than that one innocent person should be condemned and suffer capitally" (per wikipedia).
the problem with such sentiments is that we have created a system that has more concern for procedure than with justice.