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The moment of the explosion at the Boston Marathon Photo
5:39PM BST 27 Apr 2013
As they hunched over the twisted bomb parts and pieces of shrapnel, some still bloody from where they cut through flesh, the FBI technicians were finding a grimly familiar pattern. Elbow pipes from common plumbing systems. Specially-picked rounded bearings and nails of a short but disfiguring length. Gunpowder, cannibalised from the kind of large but everyday fireworks readily on sale in most American states. The precise ingredients used by the Boston bombers had been selected with rigid fealty to the instructions laid out in Inspire, al-Qaeda's online magazine which offers would-be jihadists around the world a simple path to improvising explosives. Department of Homeland Security 2010 warning on Pressure Cookers The close attention the Tsarnaev brothers appear to have paid to Inspire's detailed instructions has given new urgency to America's hunt for its editor, an unknown Islamist who goes by the name "Yahya Ibrahim". Like his predecessor, Samir Khan, who died in a drone strike in Yemen in 2011, Ibrahim appears to be a fluent English speaker; and the close match between the magazine's instructions and the bombs built by the Boston bombers appears to confirm the claim to his interrogators by Dzhokhar Tsarnaev, the surviving brother, that Inspire was critical in teaching the American-raised Chechens how to carry out their attack. But while the FBI forensic experts have the relatively straightforward task of figuring out how Tamerlan and Dzhokhar Tsarnaev managed to kill three and wounded more than 200, their investigative colleagues in Boston and 4,000 miles away in the Russian republic of Dagestan are still grappling with more confounding questions. How did these two young men - one a naturalised American citizen and the other applying to become one - grow so radicalised that they would bring Baghdad-style horror to the streets of the city in which they grew up? What, and perhaps who, drew them off the path of what seemed like an all-American story of immigrant success and into the ugly world of Islamist terrorism? Dzhokhar Tsarnaev
There are few clues in the short life of Dzhokhar, 19, who returned to his University of Massachusetts campus hours after the bombing to casually work out at the gym and party with friends. One resident of his dormitory at Pine Dale Hall said: "He seemed like just a nice kid, like one of the bros," known for habitual cigarette smoking and whose worst sin was to "push a few pounds", slang for dealing in cannabis. The door of room 7341, where he would play football videogames with a roommate and where he stashed what the FBI called "a large pyrotechnic", had last week been stripped of any markers to identify its former inhabitant. The other doors on the hall are labelled with brightly-coloured name tags. There are moments that in hindsight now seem ominous. His active Twitter feed includes jarring notes like a year-old post predicting: "I will die young". Another student recalls Dzhokhar snapping at him when he jokingly asked how to pronounce his unusual name. But almsot two weeks after the bombs were set off, the overall picture continues to be of a mild teenager, with no obvious religious faith or interest in politics. "He was the sweetest, a friendly pothead, a great student and a thoughtful guy," said Rosa Booth, a high school classmate whom Dzhokhar had once asked to be his date at a prom party. "It just doesn't make sense." In the hours after she discovered that the man she once knew had been accused of America's worst terrorist attack since September 11, Miss Booth...