Seeing as you're against the killing of innocent life, shouldn't you protest 100% of capital punishments where there is doubt?
Well, I (maybe naively) believe in our justice system. Convicted murderers are automatically given several appeals to higher courts, so I believe any of these "mistakes" are very, very rare. Convicted murderers sit on death row for years, even decades, during this appeals process, so I feel quite confident that anyone given capital punishment today actually committed the crime for which he/she is convicted. I'm sure there have been problems in the past, but I just don't believe they happen today.