If there was a way for us to actually know, 100% beyond a shadow of a doubt that person x slit person y's throat, then yes, I would support capital punishment. If anyone ever tries to kill me, I'll kill them because I'll know who it is, I won't be going to the police. But unfortunately, that's not the world we live in, there's no way we can know who killed who because the only person who knows for sure, is the person who got killed, and, alas, he's dead. So until we invent a revival machine, I'll fight the death penalty to the death.