Well there have been cases especially since DNA evidence has kicked in that would have resulted in a death penalty had it still been in force. I find it very convenient that they had a perfect record before these cases could be challenged by better technology.
There will be mistakes there are ALWAYS mistakes in the justice system. You cant bring them back to life to apologise.
They seem to have a horrific time for the rest of their lives in prison anyway.
Also in some US states they dont deal a death penalty to pedophiles because they know it will...