I believe capital punishment is heavy punishment and should have been done under very excessive crimes like murder or killing in big dimensions(massacre),when there is no expectation for saving a murder.
All of us know when a person born he is not a murder and don't want to kill or violate or rape to any body.but before any judging about a criminal first we should see what is his backgrounds and his reactions has roots in what kind of troubles.
Different research shows many criminals had family's trouble in their life and
in many times their parents didn't had a warm relation they were divorce's children and they have lots of deficits in their childhoods continuing in life without any aspiration caused they didn't follow any reasonable aims in their life and have done every things that compensate their deficits.
Basically death penalty doesn't avoid increasing violence ,when a person perpetrate a crime ,statistically, in many times know about his retribution of his crime,but the question is, why he or she have done it again?