BOSTON — The question, for all practical purposes, is no longer whether Dzhokhar Tsarnaev took part in the Boston Marathon bombing. It’s whether he deserves to die for it.

In a blunt opening statement at the nation’s biggest terrorism trial in nearly 20 years, Tsarnaev’s own lawyer flatly told a jury that the 21-year-old former college student committed the crime.

“It WAS him,” said defense attorney Judy Clarke, one of the nation’s foremost death-penalty specialists.

But in a strategy aimed at saving Tsarnaev from a death sentence, she argued that he had fallen under the malevolent influence of his now-dead older brother, Tamerlan.

“The evidence will not establish and we will not argue that Tamerlan put a gun to Dzhokhar’s head or that he forced him to join in the plan,” Clarke said, “but you will hear evidence about the kind of influence that this older brother had.”

Three people were killed and more than 260 hurt when two shrapnel-packed pressure-cooker bombs exploded near the finish line on April 15, 2013.

Tsarnaev, then 19, was accused of carrying out the attacks with 26-year-old Tamerlan, who was killed in a shootout and getaway attempt days later.

Authorities contend the brothers — ethnic Chechens who arrived from Russia more than a decade ago — were driven by anger over U.S. wars in Muslim lands.

Federal prosecutors used their opening statements, along with heartbreaking testimony and grisly video, to sketch a picture of torn-off limbs, ghastly screams, pools of blood, and the smell of sulfur and burned hair in the streets of Boston. They painted Tsarnaev as a cold-blooded killer.

Tsarnaev planted a bomb designed to “tear people apart and create a bloody spectacle,” then hung out with his college buddies as if he didn’t have a care in the world, prosecutor William Weinreb said.

“He believed that he was a soldier in a holy war against Americans,” Weinreb said. “He also believed that by winning that victory, he had taken a step toward reaching paradise.”

Among the first witnesses for the prosecution were two women who lost legs in the attack, including Rebekah Gregory, who walked slowly to the stand on an artificial limb.

“I remember being thrown back, hoisted into the air,” said Gregory, who had gone to watch the race with her 5-year-old son, Noah. “My first instinct as a mother was, where in the world was my baby, where was my son?”

She said she looked down at her leg: “My bones were literally laying next to me on the sidewalk and blood was everywhere.” She saw other peoples’ body parts all around her, and “at that point, I thought that was the day I would die.”

“I could hear Noah, I don’t know how, but I could hear my little boy. She said he was saying, ‘Mommy, Mommy, Mommy,’ over and over again.”

“I said a prayer. I said, ‘God, if this is it, take me, but let me know that Noah is OK.’”

She said someone finally picked up her son and put him down beside her. Breaking down in tears, she testified that as she looked for the boy, she saw a woman dead on the pavement.

Karen Rand McWatters, whose left leg had to be amputated, described how she watched her close friend Krystle Campbell, a 29-year-old restaurant manager, die on the pavement next to her.

“She very slowly said that her legs hurt, and we held hands, and shortly after that, her hand went limp in mine and she never spoke again after that,” she said, choking back tears.

A shaggy-haired, goateed Tsarnaev slouched in his seat and showed little reaction as the case unfolded. The defense did not ask a single question of the four victims who testified Wednesday.

About two dozen victims who came to watch the case took up an entire side of the courtroom, listening somberly to details of the carnage. Several hung their heads and appeared to fight back tears.

Prosecutors also showed the jury a gruesome video of people lying in pools of blood. The footage was punctuated by screams, moans and the crying of a boy. The ground was strewn with ball bearings and chunks of metal, and smoke wafted over the victims.

The 10 women and eight men on the jury watched somberly. Several grimaced, especially at the sight of a gaping hole in a woman’s leg.

In his opening statement, the prosecutor also described how 8-year-old Martin Richard stood on a metal barrier with other children so he could get a good view of the runners.

“The bomb tore large chunks of flesh out of Martin Richard,” and he bled to death on the sidewalk as his mother looked on helplessly, Weinreb told the jury, with the boy’s parents in the courtroom.