'Soldier in a holy war'

In his argument, Weinreb said that Dzhokhar had read radical online magazines, where he learned how to build the shrapnel-filled bombs that tore the legs off of about 16 people at the race's crowded finish line.

"He believed that he was a soldier in a holy war against Americans," Weinreb said of Tsarnaev.

The prosecutor also stressed the brutal nature of the injuries caused by the pressure-cooker bombs.

"The purpose of that kind of bomb is to shred flesh, shatter bone, set people on fire and cause people to suffer painful deaths," said Weinreb. He described the painful final moments of the three who died: restaurant manager Krystle Campbell, 29; graduate student Lingzi Lu, 23, and Martin Richard, 8.

He noted that Tsarnaev left the backpack he carried the bomb in behind a group of child spectators, including Martin.

"He pretended to be a spectator but he had murder in his heart," Weinreb said.

The prosecutor also described in detail how Dzhokhar Tsarnaev killed his brother following a gunbattle with police in the Boston suburb of Watertown, while the two were trying to flee.

"The defendant rolled right over his brother and dragged his body about 50 feet (15 meters) down the street," Weinreb said. The defendant had been trying to run down the police officers who were attempting to arrest the pair.

A dozen or so people injured in the attack and family members, including dancer Heather Abbott and Marc Fucarile, both of whom lost legs in the blasts, and Richard's parents, sat quietly in court during the proceedings.

The jury saw several videos of the bombs going off and of badly injured people screaming on the ground, surrounded by bits of metal shrapnel and thick smoke.

"I was blown through the air. There was a deafening explosion," said Colton Kilgore, who had traveled from Asheville, North Carolina, to see his mother-in-law race. "As I was sitting up my brain was in this haze and I couldn't hear out of my left ear and there was screaming and I realized ... it must have been a bomb."