Marathon bombing plot a year in making, FBI documents show

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BOSTON – Dzhokhar Tsarnaev, the convicted Boston Marathon bomber, worked with his slain brother, Tamerlan, to collect components of the two pressure-cooker bombs they used to kill three people and injure hundreds of others and didn’t tell anyone else about their plan, which may have been at least a year in the making, newly disclosed FBI documents show.

The Cambridge residents built the bombs in Tamerlan’s apartment on Norfolk Street near Inman Square, according to information from interviews with the younger brother from his Beth Israel Deaconess hospital bed where he was recovering from wounds he received during his capture April 19, 2013. According to, the FBI produced heavily redacted copies of its reports as part of a court case involving one of the bomber’s friends, Robel Phillipos, who was convicted of lying to federal investigators. Phillipos has appealed.

The younger Tsarnaev, also known as Jahar to friends, said the explosives used in the bombs came from fireworks purchased in New Hampshire starting about a year before the April 15, 2013, bombings, the FBI documents show. He told the investigators that while he went with his older brother to buy the fireworks, he didn’t know why they were making the purchases at the time.

But he soon became aware of the plan, the documents indicate.

“Only Jahar and Tamerlan were involved in the planning, procurement, construction, and detonation of the different devices,” according to the FBI documents. The agency said the pair spent $200 to buy the fireworks that supplied the explosive powder used in the bombs.

“Since he had a roommate and little privacy, Jahar did not construct any explosive devices in his college dorm room,” the FBI said, referring to Tsarnaev’s situation at the University of Massachusetts – Dartmouth, where he was a student. “However, he did leave behind one firework that he claimed was just to have some fun with by lighting off at some point.”

The brothers used instructions downloaded from a terrorist website to build their bombs, the FBI said. They set off the devices near the marathon finish line outside Copley Square hours after the winning runners had come in, thus lessening the crowd but ensuring the victims would be mostly local residents.

“Jahar stated no one had any knowledge of their plan before the attack, nor did they tell anyone after the attack had occurred,” the FBI said, adding that the surviving brother said that was “because they could not trust anyone else.”

Among the dead were an eight-year-old boy from Boston and a 29-year-old woman from Arlington, as well as a 23-year-old student from China. If any victims were Tsarnaev’s friends, that was of no concern to Jahar, the FBI said.

“Jahar did not warn any of his friends to stay away from the marathon because he didn’t care if they got hurt,” the FBI said. He described one friend, Dias Kadyrbayev, “as a ‘dumbass’,” investigators said, adding that “Jahar had a conversation with Dias about religion, how people make bombs, jihad, and the ways of the world.”

During the attack, the FBI said, each of the Tsarnaevs decided on his own where to place their bombs, which were contained in backpacks and carried to the area in Jahar’s car.

“Just before detonating his device, Jahar placed a call to his brother with the other device to try to synchronize the two detonations,” the FBI said. “After Jahar put his backpack down, he walked away and detonated the device using a button.”

Jahar returned to the UMass campus on Tuesday and stayed there through Wednesday night, the FBI said, as a massive manhunt for the bombers accelerated around Boston. While he contacted many people, none were involved in the bombings or knew of his role, the FBI said.

“On Thursday night, he contacted some of these same people to give away his laptop and other items in his dorm room as he did not expect to survive,” the FBI said. The elder Tsarnaev would die during a shootout with police late that night, and Jahar was found hiding in a boat in the backyard of a Watertown home near the site of the firefight.

He faces the death penalty.