Boston Marathon suspect boasted of his bomb-making skills: prosecutor

Boston marathon bombing suspect Dzhokhar Tsarnaev told a friend a month before the attack that he knew how to make a bomb, a US prosecutor told jurors at the friend's obstruction trial.

He also said it's good to be a martyr because you "die with a smile on your face and go straight to heaven", Assistant US Attorney Stephanie Siegmann said.

Ninety minutes after the bombing, Tsarnaev texted the friend, Azamat Tazhayakov, and said, "Don't go thinking it's me", Siegmann also told the court on Monday during opening statements at Tazhayakov's trial.

Tsarnaev is scheduled to go on trial in November on charges that carry the possibility of the death penalty. Prosecutors say he and his older brother, Tamerlan, built two bombs and placed them near the finish line of the 2013 marathon to retaliate against the US for its actions in Muslim countries. The explosions killed three people and injured more than 260. Tamerlan Tsarnaev died following a shoot-out with police days later.

Tazhayakov, 20, has pleaded not guilty to obstruction of justice and conspiracy charges. He and his roommate, Dias Kadyrbayev, went to Tsarnaev's university dormitory room several days after the bombing and took a laptop computer and a backpack containing fireworks that had black powder spilling out or had been emptied of their powder, Siegmann told the jury.

"The government will prove to you that the defendant and his co-conspirator removed the backpack … to protect their friend," Siegmann said.