Isnt committing Suicide after killing someone a way of getting away with murder?

Suicide is forbidden in (as far as I know) Judeism, Chrisitanity, and Islam......As a Muslim we believe anyone who kills themselves will be in hellfire, and they will do that act over and over to themselves in hell for eternity (they will shoot themselves, blow themselves up, etc). In Islam, killing yourself means you are despairing of Gods mercy. So, according to our religion, no they wouldnt be getting away with it, they are going to punished for eternity for it.