Listen to headcrab man, lots of people who have murdered don't even serve life sentences, so when they get out the first thing they do is rarely murder.
Because those are the people who intended to kill just one or a few people for something like a cheating wife, a best friend who slept with your girlfriend, during a domestic dispute, a neighbor you despise, etc. The people on death row are those are the ones are really forgeted up. Like Scott Peterson who was a narcissist, Richard Ramirez(rapist, serial killer, necrophiliac, Satanist, and Charles Manson who was nutty cultist that conspired to have a bunch of people get killed by his followers.