What to do?
I would favor eventually turning him over to the Iraqi government to be tried and executed. He should never leave Iraq and he should certainly not be taken to Gitmo.
There is a strong possibility that he will be put on trial in an international court. One of several problems with this is that he would not get a death sentence. I am not a DP supporter and usually that would be okay but as long as he lives he would remain a symbol for certain groups and more people might die in terrorist efforts to free him.
The Iraqis should have the privilege of ending this tyrants life.