He was given 'life' for that killing, but was paroled in 1971. These numbers speak for themselves. The Getting Away with Murder factor has been rising steadily through the years. Offenders can see that the system is easily beaten if they commit murders in any of the twelve states that do not have the death penalty. If you're truly concerned about how the criminal justice system puts innocent lives at risk, you should be demanding an end to paroles and probations.
Deterrence is a questionable argument in opposition to the death penalty.
No one has proven that the death penalty is not a deterrent. There is also no credible evidence that the death penalty is a better or worse deterrent than incarceration. But because there are so many questions about the concept of deterrence, I think it's best to look at a statement from John McAdams of Marquette University. If we execute murderers and there is in fact no deterrent effect, we have killed a bunch of murderers. If we fail to execute murderers, and doing so would in fact have deterred other murders, we have allowed the killing of a bunch of innocent victims.