What was Dzhokhar Tsarnaev like as a high-schooler? Old friend testifies.

Testimony Tuesday from one of Dzhokhar Tsarnaev's high school friends, who is facing his own legal trouble, offered a unique look into the accused bomber's life and mind-set prior to the attacks.

After more than two weeks and more than 50 prosecution witnesses, the trial of accused Boston Marathon bomber Dzhokhar Tsarnaev had provided detailed accounts of the bombings, but little insight into the defendant himself.

That began to change Tuesday. The prosecution's 60th witness, Stephen Silva, was a high school friend of Mr. Tsarnaev, and his testimony was the first time anyone who knew the defendant before the bombing had given evidence. His portrait was one of a fun-loving, pot-smoking teen with a bit of a rebellious streak and an interest in American foreign policy in the Mideast.

Mr. Silva, authorities say, was the one who gave Tsarnaev the gun that was used to kill Massachusetts Institute of Technology police officer Sean Collier in the days after the April 15, 2013, bombings.

His testimony was the product of a plea deal with federal prosecutors. Silva pleaded guilty to unrelated drug and gun charges in December, but his five-to-seven year sentence could be reduced if he cooperates with the government in the Tsarnaev trial. He was scheduled to be sentenced Tuesday, but sentencing was postponed so he could testify at Tsarnaev's trial.

Silva's attorney, Jonathan Shapiro, told reporters that his client "was not happy" about testifying against Tsarnaev, but that his client's plea deal was solid. "I'm sure the government believes he cooperated fully," he said.

Previously, both legal teams had worked to characterize Tsarnaev indirectly through two Twitter accounts and witness testimony. But Silva – who had been friends with Tsarnaev for several years at Cambridge Rindge & Latin – revealed intimate details about the defendant. Silva once described Tsarnaev to prosecutors as "one of the realest and coolest kids he ever met."

On Tuesday, Silva testified that, on a typical summer day, the two would drive around, smoke marijuana, drink, and jump off cliffs. Silva also discussed a high school class he took with Tsarnaev where they held a discussion on terrorism and American foreign policy. 

"[Dzhokhar] raised the point that American foreign policy tends to be a little hostile towards the Middle East, persecuting Muslims, going to war, trying to take over the people's culture and tell them what to do," Silva recalled Tsarnaev saying. "Americans shouldn't be allowed to go wherever they want and tell people what to do."

On cross-examination, defense attorney Miriam Conrad pressed Silva on Tsarnaev's relationship with his brother, Tamerlan, who the defense is trying to portray as the mastermind of the bombings.

Silva had testified to prosecutors that, shortly after the bombings, he had posted on Facebook that "it must have been [Tsarnaev's] brother who got him into it." Silva told Ms. Conrad Tuesday that Dzhokhar told him "his brother was very strict, very opinionated."

A flurry of objections from the prosecution stymied this line of questioning, however.

Silva acknowledged to Conrad that Tsarnaev never showed animosity towards the US, and that he celebrated Barack Obama being elected in 2012 on Twitter.

The defense also tried to get Silva to say he pressured Tsarnaev into first smoking marijuana, which would imply that Tsarnaev was vulnerable to peer pressure. Conrad pointed out that Silva had told prosecutors last August he used "peer pressure" to get Tsarnaev to smoke marijuana. But Silva backtracked on that statement Tuesday.

"I said that wrong... He chose to smoke with me," Silva told Conrad.

Silva described visiting the Tsarnaev brothers' apartment in Cambridge, Mass., in 2012 – the only time he ever visited Tsarnaev at home. He said he met Tamerlan and Tamerlan's wife, Katherine Russell, and their child. He said they watched the television show "The Walking Dead" – which Dzhokhar liked – and he saw Tsarnaev's room. The room featured a Black Standard flag – a flag often associated with Al Qaeda and jihad. A photograph taken months before the Marathon bombings appeared to show Tamerlan posing in front of the flag, and the court later released an image from Dzhokhar's Instagram account showing the younger brother posing in front of the flag.

Silva testified that he never went back to the Tsarnaevs' apartment. Conrad asked Silva why Tsarnaev didn't want him to visit the apartment, but prosecution objected and it was sustained. Conrad came back with another question.

"Did he ever say, 'You don't want to meet my brother?' " she asked.

"Yes," Silva replied.

As for the Ruger P95 9mm pistol involved in the MIT shooting, Silva said he bought it for protection after his brother was robbed of marijuana in October 2012. He testified that he gave it to Tsarnaev in February 2013, expecting to get it back "in a few weeks."

Tsarnaev then dodged questions about the gun for several weeks. "He just kept coming up with excuses," Silva testified.

Tsarnaev and Silva last saw each other in early April 2013, where Tsarnaev bought some marijuana from Silva in the parking lot of a Mobil gas station.

"I told him I loved him, and I got out the car," Silva said in court, describing the meeting. 

A few days later, Silva would learn that Tsarnaev was involved in the Boston Marathon bombings – something that he testified left him "in shock."

Silva's lawyer, Shapiro, said that Silva had no clue the gun would be used to kill a cop, and that Silva "feels badly" about Mr. Collier's murder.