Running a clandestine bomb factory in remote area in Yemen, a nondescript Saudi has emerged as the most potent threat to the United States, making three bids in past three years to spread mayhem in the world's most powerful nation.
'Underwear bomb' creator Ibrahim Hassan al-Asiri, perhaps the best bomb maker in the world, has been the most high-profile recruit of the Islamic State. And the ability of his bombs to go unchecked through the most stringent security setups has left the US and UK very worried. Vicky Nanjappa reports.