They've got him - but will he talk? Saddam Hussein could provide a wealth of information to the United States - from the fate of missing weapons of mass destruction to the funding and planning of future attacks on American troops.
Washington has said the former Iraqi dictator will be treated as a prisoner of war under the Geneva conventions. That means he cannot be forcibly interrogated. But military intelligence experts say a mix of carrots and sticks can still persuade Saddam to talk.
"It is quite amazing how big, tough people can crumple," said Ms Ellie Goldsworthy, a former British military intelligence officer who heads the UK Armed Forces Programme at the Royal United Services Institute think-tank in London.
The Geneva conventions guarantee Saddam rights that Washington has explicitly denied to hundreds of other prisoners in its "war on terror", such as the "unlawful combatants" it holds at the US prison camp in Guantanamo Bay, Cuba.
Under the third Geneva convention, the only information a fully fledged prisoner of war can be ordered to give is his name, rank, serial number and date of birth.
Mr Stephen Jakobi, of London-based rights group Fair Trials Abroad, said: "They can question him reasonably but they can use no other method of trying to get him to answer. The only information that isn't in a grey zone is information freely volunteered."
But Ms Goldsworthy said Western military interrogators receive careful training in methods that are effective in making prisoners talk, without crossing the convention's lines.
Saddam's captors will control whom he speaks to, when and for how long. They cannot deny him sleep or food, but they control what and when he eats, and when he sleeps.
"The best tactic they use is just persistence. This is one guy who is going to face countless interrogators." Interrogators can reward co-operation with improved living conditions or contact with his family.