In order to hang under international law, he must first be tried in an international tribunal. This did not happen. Moreover, his was Iraq's legitimate government and under international law there is no authority for a foreign power to depose him or his regime. Therefore, there was no legal basis for the trial or conviction.
But all that is moot, for now.
What I found to be especially compelling is the fact that certain masked people were heard to be praising Moqtada al Sadr as they executed Saddam. Obviously, they could not have been government authorities but must have been plants put there so that Sunnis could become agitated that their hero was executed by Shiites. Further violence will ensue as a consequence thereby leading to anarchic civil war. This, of course, gives Bush more excuse to prolong his war so that Halliburton and others can increase their war profiteering.
Saddam was a murderous son of a bitch who deserves no sympathy from anyone. But Pol Pot, Suharto, Mobutu, and Ne Win were far worse and they got away with their vicious sh*t without anyone batting an eye. If retributive punishment under international law is a good thing, let's not be stingy about it -- let's spread the wealth.