Vengeance is a part of justice.
Definition of VENGEANCE
: punishment inflicted in retaliation for an injury or offense
I could easily argue that life in prison is vengeance as well. My method though at least gives the victim's families some closure. Everyone knows that it won't bring back their loved ones but how can you live knowing that your child/sibling/parent is rotting in a grave while this garbage has a nice cushy bed and 3-4 square meals a day?