When Joe Darby saw the horrific photos of abuse at Abu Ghraib prison he was stunned.
So stunned that he walked out into the hot Baghdad night and smoked half a dozen cigarettes and agonised over what he should do.
Joe Darby was a reserve soldier with US forces at Abu Ghraib prison when he stumbled across those images which would eventually shock the world in 2004.
They were photographs of his colleagues, some of them men and women he had known since high school - torturing and abusing Iraqi prisoners.
His decision to hand them over rather than keep quiet changed his life forever.
The military policeman has only been allowed to talk about that struggle very recently, and in his first UK interview, for BBC Radio 4's The Choice, he told Michael Buerk how he made that decision and how he fears for the safety of his family.
