Then his defense lawyer told a jury during opening statements last month that "it was him."
All that was left for the jury of seven women and five men to do was to find him guilty on the 30 counts he faced. They did so swiftly, convicting him on every count Wednesday, including 17 that carry the death penalty.
It took the jury more than 11 hours over two days to reach its verdict, less than half the time it took for a jury to convict Timothy McVeigh in the bombing of the Murrah Federal Building in Oklahoma City.
READ ALSO: Fate of Boston bomber, Dzhokhar Tsarnaev in the hands of US jury
Whether Tsarnaev is sentenced to life in prison without the possibility of parole or dies by lethal injection will be decided later this month when the same jury returns to conclude the portion of the trial known as the penalty phase.
Among the most serious charges, Tsarnaev was convicted of using a weapon of mass destruction that resulted in the deaths of three people in the attack two years ago and, separately, of killing Sean Collier, a Massachusetts Institute of Technology police officer.
As the verdict was read at a federal courthouse at the Boston Harbor, Tsarnaev stood between his lawyers and listened impassively. He clasped his hands together and gazed down or straight ahead, avoiding eye contact with the jury.
In this courtroom sketch, Dzhokhar Tsarnaev, (second, left) is depicted standing with his defense attorneys William Fick, left, Judy Clarke (second, right) and David Bruck (right) as the jury presents its verdict. - AP Photo/Jane Flavell Collins
When it was over, he left the courtroom without incident. Survivors and victims' families — many of whom sat through weeks of sometimes wrenching testimony — shuffled out.
"Today isn't a happy occasion, but it's another chance to put things behind us," Karen Brassard, who was wounded in one of the blasts, said afterward. She summed up what many thought while looking at Tsarnaev over the course of the trial: "I don't believe there is any remorse."
In a statement, Collier's family thanked the FBI and federal prosecutors for their work in obtaining a conviction. They also had a message for Tsarnaev, a wayward college dropout who embraced radical Islam with such violent fervor that he carried out one of the worst acts of terrorism on U.S. soil since Sept. 11, 2001.
"The strength and bond that everyone has shown during these last two years proves that if these terrorists thought they would somehow strike fear in the hearts of people, they monumentally failed," the family said.
The guilty verdicts come a week before the anniversary of the bombings and more than a month after one of Tsarnaev's defense attorneys, Judy Clarke, told the jury that her client had carried out the bombings with his brother, Tamerlan Tsarnaev, 26, who was killed after a shootout with police.
Clarke had argued that it was Tamerlan who engineered the bombing and also radicalized and dominated his younger brother, who, she said, does not share the same level of culpability.
"We don't deny that Jahar fully participated in the events," she told the jury, using Dzhokhar's nickname. "But if not for Tamerlan, it would not have happened."
The prosecution had dismissed that line of defense and repeatedly told the jury that the brothers were a team interested in punishing Americans for the wars in Iraq and Afghanistan. Assistant U.S. Attorney William Weinreb said blaming the older brother was an attempt to "dodge responsibility for what he did."
Prosecutors described the former college student's plan as "a cold, calculated terrorist act" that was "bloodthirsty."
"To shred the bodies of young women and children with a homemade bomb, you've got to be different from other people," Weinreb said during closing arguments.
The government called more than 90 witnesses during the trial, which began with opening statements March 4. Prosecutors methodically described the construction of two pressure-cooker bombs packed with shrapnel that were placed near the finish line April 15, 2013, and the horrifying destruction when they exploded among the crowds watching the race on Boylston Street.
More than 260 people were injured when the bombs detonated within seconds of each other; 17 people lost limbs. The bombings jolted the country and scarred a proud city.
"I am thankful that this phase of the trial has come to an end and am hopeful for a swift sentencing process," Boston Mayor Martin Walsh said after the verdict. "The incidents of those days have forever left a mark on our city."
During the trial, prosecutors played a video of Tsarnaev planting one of the bombs near 8-year-old Martin Richard, whose body, they said, was "destroyed" in the blast.
"His entire body was shattered. It was broken, eviscerated, burned," Assistant U.S. Attorney Aloke Chakravarty said. "There wasn't a part of this boy's body that wasn't destroyed."
Clarke tried to play down the video by saying that her client intentionally put the bomb next to a tree — not the boy. That is likely to be a crucial point of contention in the sentencing phase because Martin's age will probably be cited by prosecutors as an aggravating factor in support of the death penalty.
Prosecutors said they could not say definitively which brother shot and killed Collier but told the jury that as a matter of law they were equally culpable.
"They knew exactly what they were going to do. They must have planned it ahead of time. It was a cold-blooded execution," Weinreb said.
Prosecutors also described how the brothers carjacked a man driving a Mercedes after they were identified as suspects. They then fled to Watertown, Massachusetts, where police finally confronted them. Armed with a 9mm handgun, Tsarnaev fired 56 times and both brothers tossed pipe bombs at the police, prosecutors said.
The older brother was killed during the confrontation, but the younger Tsarnaev escaped. He was later discovered wounded and hiding in a boat in a nearby back yard, where he wrote a note that prosecutors have described as a confession. He also carved a line in the boat: "Stop killing our innocent people and we will stop."
