Capital punishment is a very cloudy area... nothing is in black and white.
On the one hand, if someone has been proven beyond all doubt that they have taken a human life, why do we not make an example of them and save the system some cell space by taking their life?
Maybe it's a transition from Old Testament justice, (an eye for an eye) to New Testament/Ghandi justice (and eye for an eye will make us all blind, turn the other cheek), that we do not have the right to take away a human (God's?) life.
We might also be becoming more understanding that even if there is seemingly absolute proof that someone is guilty there could be new evidence found somwhere along the line which would have reversed the verdict.
Personally, I think we should leave them to rot in prison until the day the die, whereupon they can be judged a second time.
Big Richard - Longer sentences aren't much of a deterrent; nobody plans on getting caught.