Boston Marathon Bombing Trial: Friend Says He Gave Tsarnaev a Gun Later Used to Kill Cop

— -- A long-time friend of the alleged Boston Marathon bomber testified in court today that he gave Dzhokhar Tsarnaev the gun later used in the shooting death of an MIT police officer.

Stephen Silva, 21, told the court that he would consider Tsarnaev "one of my best friends."

Silva is currently in prison after signing a plea deal with the government. He was the subject of an undercover federal investigation last year and pleaded guilty to charges including distribution of heroin, and possession of a firearm with an obliterated serial number. While wearing a beige prison jumpsuit, Silva testified that two months before the bombings at the Boston Marathon finish line, he gave Tsarnaev a 9-millimeter handgun that had an "obliterated" serial number.

The gun was later used in the fatal shooting of MIT Police Officer Sean Collier, according to prosecutors, and during a shootout between Tsarnaev and police.

Tsarnaev, Silva said, told him he wanted to use the gun "for a rip" -- a robbery.

Silva also testified about an incident in high school, when a teacher asked if terrorism is ever justifiable.

Silva testified that Tsarnaev said, "American foreign policy tends to be hostile ... trying to take over people's culture."

Defense lawyers used the opportunity to elicit testimony that backed up their assertion that Tsarnaev was under the influence of his older brother, Tamerlan Tsarnaev, and that he was not himself a committed terrorist.

Under questioning by Tsarnaev's defense attorney, Miriam Conrad, Silva said that Tsarnaev "talked religion not in depth, not all the time" and described the suspect as not-violent and well liked. Conrad also emphasized that the pair enjoyed "typical teenage things," like jumping off cliffs at a local reservoir. In one dramatic moment, Silva was reminded by Conrad that Tsarnaev once told him, "You don’t want to meet my brother."

"He said his brother was very strict, very opinionated," Silva testified. "And that since I wasn't a Muslim he might give me a little s*** for that."

A Cambridge man mentioned in Silva's testimony made an appearance at the same federal courthouse in Boston today. Merhawi "Howie" Berhe was indicted last week on federal charges relating to the possession of the Ruger P95 handgun later used by the Tsarnaev brothers, according to the indictment.

Berhe, Silva testified today, gave him the gun because "his mother had searched his room and he needed to get it out of his house." Silva described using the gun to rip off two men in Cambridge, and said he brought it to a New Year's Eve party in Medford in 2012 before he lent it to Tsarnaev.

Berhe appeared for a detention hearing today at the same time Silva was taking the stand in the bombing trial. Berhe was freed on bail and his lawyer told ABC News he could not discuss his client's case, except to say that Berhe had been released "with conditions."

In Tsarnaev's trial, a new picture was also introduced at the trial showing the Tsarnaev posing under a black flag with white and black Arabic writing. Similar flags have sometimes been associated with jihad, but this has not been independently confirmed by ABC News.

The prosecution claimed the flag hung in Dzhokhar Tsarnaev's bedroom.

Earlier in the today's trial, a Massachusetts man recounted the terrifying moment he realized the Tsarnaev was hiding in a boat in his backyard.

David Henneberry testified that he "kept fixating" on a pool of blood that he discovered on the deck of his boat, the "Slipaway II," that was in his backyard.

The retiree testified that he checked on the boat after two chafing guards and the shrink wrap had fallen off the boat.

"Not a huge amount," he said of the blood he saw on the boat deck. "But enough."

When he climbed a ladder, he "saw a body in the boat," Henneberry told the court, also describing Dzhokhar Tsarnaev's shoes, pants and hooded sweatshirt.

There was "no movement at all" from the figure "lying on his side," he testified.

Tsarnaev had been on the run since a shootout hours earlier with police that left his brother dead and an officer injured, according to prosecutors.

The prosecution also showed pictures of the message that they said Tsarnaev scrawled on to the side of the boat. The prosecution also introduced into evidence the bloodied pencil that authorities said Tsarnaev used.

The message "Stop killing our innocent people ... we will stop," was carved into a wooden slat on the side of the boat. Tsarnaev also scrawled a long message in pencil branded with the name of David Henneberry's stepson's company, according to the prosecution.

Tsarnaev faces the death penalty for his role in the 2013 Boston Marathon bombings that killed three people. Am MIT police officer was killed days later, allegedly by Tsarnaev and his older brother Tamerlan Tsarnaev.

During Monday's court proceedings, a number of police officers described the gunfight between cops and the Tsarnaev brothers and the ensuing struggle with Tamerlan Tsarnaev. They also testified that Dzhokhar Tsarnaev sped in an SUV toward the struggle, ultimately running over his older brother.

Dzhokhar Tsarnaev has pleaded not guilty to the 30 counts against him, including charges of using a "weapon of mass destruction resulting in death," but his defense attorney has said that he participated in the bombing.