And when did I say it was an effective deterrent? Capital Punishments purpose is not to deter crime, but rather to punish one.
Canada abolished the death penalty years ago, there was no increase in murders, but murder convictions doubled, since they speculate, the jury was not making a life or death decision.
So, more convictions .. hmmmm. I tend to view imprisonment for a reprehensible murder to be somewhat of a refuge or sanctuary.