What should be the punishment for a person who commits murder while already serving a life-without-parole sentence?

What should be the punishment for a person who commits murder while already serving a life-without-parole sentence?

Mike Farrell (President, Death Penalty Focus) gives expert video advice on: What is the main moral argument used to promote the death penalty?; What is your moral perspective on the death penalty?; What do abolitionists say to the families of murder victims? and more...