Jane Flavell Collins, Associated Press
In this courtroom sketch, Dun Meng, far right, testifies with a translator at his side during the federal death penalty trial of Boston Marathon bombing suspect Dzhokhar Tsarnaev in Boston, Thursday, March 12, 2015. Meng described his harrowing ride at gunpoint with the Boston Marathon bombers and the moment he made "the most difficult decision" of his life to bolt from the car.

BOSTON — A lawyer for Boston Marathon bomber Dzhokhar Tsarnaev aggressively questioned an FBI agent Monday about extremist materials found on Tsarnaev's computer as the defense attempted to portray his brother as more radicalized and primarily responsible for the 2013 attack.

Kevin Swindon, a supervisory agent in charge of the Boston FBI's cybersquad, last week described a variety of extremist content found on Tsarnaev's computer, including an article called "Make a Bomb in the Kitchen of Your Mom" in an issue of Inspire, an al-Qaida publication.

During cross-examination Monday by defense attorney William Fick, Swindon acknowledged that Tamerlan Tsarnaev's computer had encryption software on it, but Dzhokhar's computer did not, an apparent attempt by the defense to suggest that Tamerlan had something to hide.

Tsarnaev's lawyers acknowledged during opening statements that Dzhokhar, now 21, participated in the bombings but said it was Tamerlan, 26, who was the mastermind and recruited his impressionable younger brother to help him.

While questioning Swindon, Fick also suggested that much of the activity on Dzhokhar's computer centered on Facebook and other subjects of interest to teenage boys, including popular music and homework. As part of one of his questions, Fick said there was nothing about "jihad" or "Islam" among the top search terms on Dzhokhar's computer.

Twin pressure-cooker bombs planted at the finish line of the 2013 marathon killed three people and injured more than 260.

Authorities say the Tsarnaev brothers carried out the attack to retaliate against the U.S. for wars in Muslim countries. Tamerlan died days after the bombings after a gunfight with police.

If convicted, Dzhokhar Tsarnaev faces the possibility of the death penalty.