Investigators are trying to establish a motive for the Boston Marathon bombings.
Specialist teams are waiting to interview Dzhokhar Tsarnaev, the 19 year-old suspected of carrying out the attack.
The young man is seriously injured in a Boston hospital, after he was captured late on Friday following a huge manhunt.
His elder brother, Tamerlan, was killed in a shootout with police.
A picture of Dzhokhar as a likable, sociable young man is emerging.
He was known at the local mosque, but was by no means devout:
Anwar Kazmi is from the student’s local mosque in Boston:
“We can only describe him as an infrequent visitor. And when I say visitor, I mean he would come here for the Friday prayers, and this happened only within the last year and a half or so”.
Austin Hightower, is a fellow student and friend of Dzhokhar:
“He was just the nicest guy. He liked a smoke, he liked girls, he drank at some of the parties he came down, so he wasn’t a loner, he was definitely social. That’s why I can’t make sense of it.”
Dzhokar was hiding in a boat in the suburb of Watertown when he was apprehended after the vessel’s owner spotted blood on the boat and called the police.
The student was shot in the throat and cannot speak due to injuries to his tongue.
It has emerged that elder brother Tamerlan had been interviewed by the FBI in 2011 after Russian security services raised concerns that he was a follower of radical Islam.
The FBI said no evidence of terrorist activity was found at the time.