I go back and forth on the death penalty. Here in Washington State, because of the Green River killer's no death penalty, it is pretty far-fetched that anyone would get it now. (Ladies and gentlemen of the jury, my client only killed 6 people, while the Green River killer killed dozens and gets to live).
The cost (to the state) on actually getting to the death penalty carried out I've heard is more than just keeping the guy in for life (attorney's fees).
I think life in prison is the worst you can do to somebody - solitary, no TV, no books, etc.
However - you do bring up a very good point that the death penalty can bring more cases to be solved (like the Green River Killer). I imagine if we made for swifter sentencings and execution it might be a deterrent - but I wonder how many of these guys think they will get caught in the first place?
They all think they are too smart to get caught and have no idea just how dogged cops are when trying to solve a murder.