Defense attorneys have admitted that the 21-year-old defendant committed the crimes he is accused of, but are trying to save his life in the capital case by arguing that his brother masterminded the attacks.

FBI computer specialist Kevin Swindon testified earlier that copies of Al-Qaida's "Inspire" magazine were found on Tsarnaev's laptop, including one with an article titled: "How to Make a Bomb in the Kitchen of Your Mom." It also included several audio files of Awlaki lectures, he said.

Swindon said the laptop also had backup files of Tsarnaev's iPhone that showed he texted a friend, Dias Kadyrbayev, shortly after the attack, saying: "U saw the news?... Better not text me my friend."

Defense attorney William Fick grilled Swindon in cross-examination in an attempt to point out that it was unclear where the files on Tsarnaev's computer originated, and that there was a chance that some were placed there by Tamerlan or others.

Fick asked Swindon about a thumb drive investigators had found at a landfill along with other items belonging to Dzhokhar, which contained files on how to make explosives: "Isn't it true that every file and folder on this drive was created by Tamerlan's computer?"

"I don't know," Swindon replied.

Separately, a poll released on Monday found that more Boston-area residents would prefer to see Tsarnaev sentenced to life in prison without the possibility of parole rather than death. Some 49 percent of respondents to a poll conducted for WBUR radio by MassInc Polling said they preferred a life sentence, with 38 percent wanting to see a death sentence.

The bombing killed restaurant manager Krystle Campbell, 29, graduate student Lingzi Lu, 23, and 8-year-old Martin Richard. Massachusetts Institute of Technology police officer Sean Collier, 27, was shot dead three days later.