Dzhokhar Tsarnaev is pictured in this handout photo presented as evidence by the U.S. Attorney's Office in Boston, Massachusetts on March 23, 2015. REUTERS/U.S. ATTORNEY'S OFFICE IN BOSTON/HANDOUT VIA REUTERS

(Reuters) - Lawyers for accused Boston Marathon bomber Dzhokhar Tsarnaev and a terrorism expert serving as a prosecution witness argued on Tuesday over whether the defendant was paraphrasing Al Qaeda propaganda in a note he left four days after the deadly attack.

While hiding in a boat hours before his arrest, Tsarnaev scrawled a note reading, in part, "we Muslims are one body you hurt one you hurt us all," a message counter-terrorism expert Matthew Levitt said was similar to extremist writings found on Tsarnaev's computer.

Defense attorney David Bruck asked Levitt if it was not possible that Tsarnaev, now 21, had heard those words from his older brother, Tamerlan.

"Could other people have hit these points too? Maybe in that same verbatim language? Maybe," Levitt acknowledged at U.S. District Court in Boston. "Could that have contributed to the radicalization? It could have."

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 tried to flee.

Tamerlan died hours after the shooting, following a gunfight with police.

Defense attorneys opened Dzhokhar Tsarnaev's trial March 5 admitting he committed the crimes, but are seeking to persuade the jury to spare him the death penalty by painting him as a mostly normal American kid who fell under his brother's spell.

Levitt, a senior fellow at a Washington think-tank and a former U.S. intelligence agent, told jurors he did not know if the materials found on Tsarnaev’s computer, including sermons by U.S.-born Al Qaeda figure Anwar al-Awlaki and issues of Al Qaeda’s "Inspire" magazine, were put there by Tsarnaev or by someone else, such as his brother.


The jury also saw records of the younger Tsarnaev taking target practice at a New Hampshire shooting range about a month before the bombing. Dzhokhar Tsarnaev paid about $170 to rent two 9 mm Glock handguns, which use the same sort of ammunition used to fatally shoot Massachusetts Institute of Technology police officer Sean Collier on April 18, 2013.

FBI special agent Matthew Riportella testified that Dzhokhar Tsarnaev, not Tamerlan, rented the guns and listed himself as having "intermediate" firearms experience on a form there.

Jurors also saw images of deformed bullets recovered from Collier's head, as well as a single shell casing almost submerged in a pool of bright red blood in the driver’s seat of the officer's cruiser.

David Cahill, a lieutenant with the Massachusetts State Police, testified that 56 of 266 shell casings recovered after the gunfight were consistent with a black 9 mm Ruger found at the scene in Watertown, a suburb of Boston. It was fitted with an extended magazine able to hold 18 bullets, not just the usual 10, he added.

Bullets from that gun, lent to Tsarnaev by a friend, are believed to be the ones that killed Collier.

Prosecutors acknowledge they are not sure which of the brothers pulled the trigger during the ambush of Collier, but contend both were present and equally guilty.

The Tsarnaevs, ethnic Chechens, immigrated to the United States from Russia a decade before the attack and settled in Cambridge, Massachusetts, just outside Boston.

Separately, Khairullozhon Matanov, a citizen of Kyrgyzstan, is due to plead guilty on Tuesday on charges of lying to investigators probing the bombing. The man was a friend of the Tsarnaevs but played down how well he knew them.

The bombing killed restaurant manager Krystle Campbell, 29, graduate student Lingzi Lu, 23, and 8-year-old Martin Richard.