Not let him get away with, life-time jail or something near it. I do not call death penalty a punishment.
For those who fear death more than anything else, then it would be. For those who don't, then giving them a lifetime of suffering would be more suitable.
However, I believe it is an absurd injustice if your taxpayer money goes to feed, clothe, and shelter the very same criminal who murdered your entire family. There is no justice for the victims and their families in that case.