How many innocent people is it okay to put to death? You'll note that I'm not saying that either of the examples that you gave are innocent people, but innocent people are put to death, so: how many?
This isn't a trick question. It's not okay to say, well, ideally there should be none. I'm asking right now since you think we should be hanging people in the public square.
The death penalty necessarily means in our imperfect information world that innocent people will be put to death. So there's no bright line for anything that we can point to and say that's how you do it.
It is also not okay to say that they exhausted all avenues of the justice system available to them and unfortunately it didn't work and them's the breaks kid.
So how many innocent people is it okay to put to death?