Boston bomb accused's lawyer: He did it

A courtroom sketch of defence lawyer Judy Clarke and USDistrict Court judge George O'Toole on the first day of the trial. Photo / AP

A lawyer for accused Boston Marathon bomber Dzhokhar Tsarnaev told a jury that her client and his brother carried out the deadly attack almost two years ago.

"It was him," Judy Clarke said in her opening statement at the trial in Boston federal court. Calling the events of April 2013 "incomprehensible" and "inexcusable", Clarke said they were "caused by a series of senseless, horrible misguided acts carried out by two brothers".

By admitting that Tsarnaev took part in the attack, in which three people were killed and 260 injured, the defence is setting the stage for the second phase of the trial, in which a jury must determine whether the defendant should be executed.

In shifting much of the blame to Tsarnaev's older brother, Clarke is seeking to save her client's life. Tamerlan Tsarnaev, an alleged radical Muslim, died in a shootout with police days after the attack.

"It was Tamerlan Tsarnaev who self-radicalised," Clarke told the jury. "It was Dzhokhar who followed him."

The Government has said Tsarnaev and his brother planned the attack to avenge Muslims killed by US forces overseas.

Victims and their families arrived by the busload for the trial. Some filled the first five rows of the courtroom. Others followed it on a monitor in another part of the building.

Assistant US Attorney William Weinreb painted the defendant as someone who could take part in a deadly terrorist attack one moment, and blithely go about his business the next.

"When he was with his friends, he played video games. When he was by himself, he read terrorist writings and watched terrorist lectures."

Twenty minutes after the brothers set off two home-made bombs near the marathon finish line, Dzhokhar went to a grocery store to buy milk, Weinreb said.

"While victims of the bombing lay in the hospital learning that they may have to have their limbs cut off ... the defendant acted as if nothing had happened," Weinreb said.

Weinreb also sought to pre-empt defence arguments that Dzhokhar was in his brother's thrall.

"Even though he and his brother had different roles in committing these crimes, they were equally guilty," he said.

"The defendant's goal that day was to maim and kill as many victims as possible. He pretended to be a spectator but he had murder in his heart.

- Washington Post-Bloomberg