Court documents, released Wednesday, indicate that the brothers accused of detonating bombs at the finish line of the Boston Marathon used “relatively sophisticated” bombs made with remote-control detonators taken from model car parts and fuses made from Christmas lights.
Prosecutors also said in the documents that Tamerlan and Dzhokhar Tsarnaev crushed numerous fireworks to remove fine black powder in order to build the deadly explosives.
Dzhokhar Tsarnaev is awaiting trial, and possibly facing the death penalty, for his role in the 2013 attack on the Boston Marathon that killed three people and injured more than 260. His brother, Tamerlan, was killed by police in a shootout after a four-day manhunt that followed the attack.
The prosecution filed the documents with the court to counter a defense motion to throw out statements Tsarnaev made to the FBI without the benefit of a lawyer.
The prosecution contends that, because of the sophistication of the bombs, the agents had reason to believe that other co-conspirators were still on the loose and there was a threat of more attacks.
"The Marathon bombs were constructed using improvised fuses made from Christmas lights and improvised, remote-control detonators fashioned from model car parts,” read the documents obtained by CNN. "These relatively sophisticated devices would have been difficult for the Tsarnaevs to fabricate successfully without training or assistance from others.”
Fox News reports that earlier this month defense attorneys argued that statements Tsarnaev made to agents in the 36 hours after his arrest, before a lawyer was present, should not be allowed in court. The lawyers said agents continued questioning him "despite the fact that he quickly allayed concerns about any continuing threat to public safety, repeatedly asked for a lawyer, and begged to rest.” They also said his treatment included heavy painkillers that could have impaired his judgement.
The prosecution contends Tsarnaev was questioned under the so-called public safety exception which allows an interrogation to happen prior to Miranda rights being read or a lawyer being present if investigators fear another attack is imminent.
"In light of the history of coordinated terrorist attacks … the FBI had a duty to be investigate whether any additional attacks were imminent," the prosecution’s filing said. "Interviewing Tsarnaev as soon as possible was therefore essential to protect the public from possible harm.”
Tsarnaev has pleaded not guilty to several federal charges against him. His defense attorneys have filed a motion asking that the death penalty be declared unconstitutional. They have also asked that some of the aggravating factors cited by prosecutors as justification for seeking the death penalty be thrown out. Decisions on those motions are pending.
Jury selection has not yet begun and no trial date has been set.