A man who successfully punches someone with the intent to kill them is morally equal to a man who unsuccessfully punches someone with the intent to kill him.
A man who successfully punches someone with the intent to kill them is morally worse than a man who punches someone without intent to kill them, but kills them anyway.
How the law treats each case should be informed by, but not not necessarily follow, these rules of thumb, for the reasons Berni articulates elsewhere in this thread.