The death penalty would've spared him of so many years of suffering in a prison cell. I don't think you want that, do you?

To play devil's advocate, there are two real good reasons for the death penalty:

1. It's the humane thing to do, if we have no choice but to jail someone indefinitely with no hope for redemption.

2. Tax money could be used somewhere else, like improving the lives of the poor and providing mental care services to help people before they get into trouble