Actual execution seems to be a bigger deterrent to people committing murder rather than I go to prison, learn to adapt, maybe actually get out someday for some screwball reason.
When someone receives the death penalty the appeal process needs to be seriously speeded up. Years and years on death row is ridiculous. One year tops and then fry them PUBLICLY. Another deterrent. I wouldn't even mind putting them to death the same way they killed others. Susan Smith drowned her children? Put her in a car and roll her in and out of a river a dozen times before actually leaving her in for the final time. Dumb bitch. Killing her children because of a man.