Erm, I don't think Sadaam couldn't have been tried for war crimes without an invasion. Do you honestly think he would have surrended to the United Nations to be put on trial for anything? I'm surprised he even let UN weapons inspectors in. The only way to get rid of Sadaam once and for all was to either launch a stealth attack and take him out (extremely difficult, especially given the number of doubles and sons/generals etc. he has), or to invade the country and hunt him until he was caught.