I found myself unable to answer the question because of the amazing second part.
What should happen to him?
He should be tried by the Iraqis. At the end of the trial, if found guilty, he should receive the appropriate sentence. In his case, this may very well be the death sentence. Not sure what form that takes in Iraq, but I think it will be a) pretty swift and b) not subject to endless appeals and stays of execution.
During the first Gulf war, the British captured the notorious Iraqi torturer Abu Tuwaguz. In return for working for the British and spying on the regime, he was flown back to the UK after the war, and now lives in Surrey in a 10 bedroom house.