Abu Bakr al-Baghdadi: Why is it so difficult to track down IS leader?

"He learned a lot on how to operate from Saddam's former intelligence officials," says Michael Stephens, a Middle East expert with the London-based think-tank Royal United Services Institute (Rusi). "His operational security is excellent," he adds, "partly because of his excessive paranoia". Where is he hiding now? Almost certainly still in the Iraq-Syria border area, says Stephens. "He'll be able to take advantage of established smuggling networks across that border," he says, "using money to pay his way amongst the tribes there".