A still image from surveillance video and entered as evidence shows Boston Marathon bombing suspect Dzhokhar Tsarnaev, in this handout photo provided by the US Attorney's Office in Boston, Massachusetts, on March 11, 2015. [Photo/Agencies]

BOSTON - Boston Marathon bombing suspect Dzhokhar Tsarnaev was heavily influenced by Al-Qaida literature and lectures, some of which was found on his laptop, a counterterrorism expert testified at his trial on Monday.

The testimony cut to the heart one of America's most closely watched court battles, with prosecutors painting Tsarnaev as a home-grown terrorist and his defense arguing he was a mostly normal American kid who came under the influence of his radical older brother.

Matthew Levitt, a senior fellow at the Washington Institute for Near East Studies, said some of Tsarnaev's Twitter posts and parts of a note he scrawled inside a drydocked boat where he was captured several days after the deadly marathon attack resembled Islamist publications.

"We see in them (concepts from) al-Awlaki's statements and other writings from the radicalizers," Levitt said, referring to Anwar al-Awlaki, a US-born Al-Qaida figure who published lectures and a glossy English-language magazine about violent jihad found on Tsarnaev's computer.

Awlaki was killed in a US drone strike in 2011.

Levitt added that the marathon bombing appeared to fit into a broader "global jihad movement" that encourages Muslims to commit violence targeting the United States.

Tsarnaev is accused of killing three people and injuring 264 with a pair of homemade pressure-cooker bombs at the race's crowded finish line on April 15, 2013, and with fatally shooting a police officer three days later as he and his 26-year-old brother, Tamerlan, tried to flee the city.

Tamerlan Tsarnaev died following a gunfight with police later that night and Dzhokhar was arrested, severely wounded by gunfire, after a homeowner in the suburb of Watertown found him hiding in a boat in his backyard. He left a note in that boat suggesting that the attacks were an act of retribution for US military campaigns in Muslim-dominated countries and that he viewed his brother as a martyr.