U.S. prosecutors say Tsarnaev, 21, and his brother, Tamerlan, 26, were the two people seen hurrying down Boylston Street in video taken by store surveillance cameras after allegedly leaving two homemade pressure-cooker bombs on the crowded sidewalk near the race’s end.
The bombs exploded 12 seconds apart, forcing cancellation of the 2013 race.
Tsarnaev pleaded innocent to all charges, according to the Reuters news service.
Tamerlan was killed a few days later in a shootout with police in nearby Watertown, where Tsarnaev was eventually found hiding.
Tsarnaev faces a 30-count indictment including fatally shooting a campus police officer at Massachusetts Institute of Technology in Cambridge during the brothers’ escape attempt.
On Monday, prosecutors advised U.S. District Court Judge George O’Toole that they may want to introduce autopsy photos of Martin Richard, 8, the youngest victim of the bombing, as evidence in the trial.
Government attorneys also said they wanted to use video clips from a televised news conference at which Tsarnaev and his brother were identified publicly for the first time, leading to the start of a massive search and an all-day lockdown of most of the Boston area.
But defense attorneys say Tsarnaev was being heavily influenced by Tamerlan, who they contend was the mastermind of the bombing.
A jury of 10 women and eight men, all of them white, have been selected to hear the case, which is expected to continue through June, Reuters said.
The jury also is charged with recommending the penalty of death or life in prison without possibility of parole.
Sixteen of the injured had limbs amputated, Reuters said.
Killed in the bombing were restaurant manager Krystle Campbell, 29; graduate student Lingzi Lu, 23, and Martin Richard.
The MIT police officer, Sean Collier, 27, was killed three days after the bombing.
