Tamerlan, the eldest, started hearing the voice as a young man. It disturbed him. It frightened him, as the voice inside grew more insistent. It may in the end have directed him.
Dzhokhar, the youngest, was the child full of promise. But almost from the moment he left home, trouble and failure seemed to mark him, and risk to allure him. He was anything but a passive figure in the history the brothers would soon make.
A five-month Globe investigation offers new details and insights into the two young men accused in the greatest act of terrorism in Boston history and the deeply dysfunctional family that produced them.