Explain this to me.
You are a hired murderer. You attempt to kill somebody and fail, but get caught. You get, let's say, 5 years in prison.
You are a hired murderer. You kill your target, get caught and get the death penalty.
The intent in both cases was the same. I believe the intended murderer who bungled the job should get the same punishment as the murderer who was successful. You are dealing with the same person with the only difference being that one was a bungling fool. If he hadn't bungled the job someone would be dead and he would rightfully (in some states in the U.S.) get the death penalty.