Dzhokhar, who was traced in a seriously injured condition following a massive manhunt which had shut Boston down last Friday, said there was no international group involved in the attack which killed three people besides injuring nearly 180 people and that he and his brother acted alone in carrying out the attacks.
One policeman was also killed later at the Massachusetts Institute of Technology campus during a gunfire between the two brothers and the security personnel.
The 19-year-old could not speak owing to throat injury and was responding to the sleuths in writing.
According to a report, government officials said that the two brothers were self-radicalised jihadists, preliminary investigation suggested. The investigators would also interrogate widow of Tamerlan, although she said that she knew nothing about the attack.
Dzhokhar, however, could face death penalty after being charged for his alleged involvement in the deadly bombings. One of the three killed in the blasts was an eight-year-old boy. If Dzhokhar, a naturalised US citizen of Chechen descent, is convicted of federal charges, he would be imprisoned or even sent to the gallows.
The US citizens on Monday observed a moment of silence to mark a week of the bombings, from the White House to the New York Stock Exchange.