By all accounts, the paths traveled by the Tsarnaev brothers in their new American lives had begun to diverge. Tamerlan, 26, the elder brother, turned more deeply to his Muslim faith as once-promising boxing prospects faded. Dzhokhar, seven years his junior, won a college scholarship, gained U.S. citizenship and was seen by friends as embracing the opportunities of his new country.
Still, their lives were far more tightly bound than outsiders might have perceived. They shared a dark, secret connection until the moment that the FBI posted their images as the terrorists suspected of making and detonating twin pressure-cooker bombs near the finish line of the Boston Marathon on April 15.
Such sibling plotting — which is particularly difficult for law enforcement personnel to detect — has precedents, said John Horgan, director of the International Center for the Study of Terrorism at Pennsylvania State University. In such instances, siblings aren't inclined to confide in outsiders, making their plans more covert than actions by a loose-lipped "lone wolf" operator or a terrorist cell, he said.