On the prowl for WMD

i was wondering the other day... how can it be legal to launch all those missiles on that bunker the first day, with the admitted intention of killing Saddam Hussein and his sons and others with him?

i dont understand what the legal basis is for intentionally trying to kill him even before hostilities began. is it just because he is in a bunker and that is a legitimate military target?

i noticed the world was pretty quiet about it. so i am thinking i am missing something.