The death penalty isn't really (or shouldn't really) be about punishment. It should be about removing a threat to innocent lives. As in...if the guy on death row would, if freed, go kill someone, then perhaps killing him is the best thing for everybody.
Me...I'm nastier than that. I do believe in punishment. I want people who deliberately commit murder to spend a very long time in a concrete cell. With nothing to do. Nobody to talk to. For the rest of, hopefully, a very long life.
I do NOT believe that a deliberate murderer (especially one whose motive is not , er, 'personal,' will ever be safe to let out on the streets, so something has to be done about him or her to make certain that opportunity never exists again. IMO, the death penalty is the easy way out.
But...I'm vindictive, as I mentioned. No death penalty.