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The accused Boston Marathon bombers used powder from crushed fireworks, fuses made from Christmas lights and detonators assembled from model car parts to construct their bombs, prosecutors allege in new court documents.

The documents — filed in opposition to a motion to suppress the evidence from lawyers for Dzhokar Tsarnaev — confirm an exclusive report last year by NBC News that federal prosecutors believe Tsarnaev and his brother Tamerlan closely followed a bombmaking process detailed in the digital al Qaeda magazine “Inspire.”

Tamerlan Tsarnaev died on his way to the hospital after the bombings in April 2013. Dzhokar Tsarnaev is charged with using a weapon of mass destruction resulting in the deaths of a boy and three other people.

Prosecutors claim that the sophistication of the explosive devices that went off at the finish line of the marathon indicates the Tsarnaev brothers had received training or help from others.

"The Marathon bombs were constructed using improvised fuses made from Christmas lights and improvised, remote-control detonators fashioned from model car parts. These relatively sophisticated devices would have been difficult for the Tsarnaevs to fabricate successfully without training or assistance from others," court documents read, detailing the information first reported by NBC News.

In addition, prosecutors said searches of Tsarnaevs' homes, cars and other locations that they were associated with found no traces of black powder, "suggesting that others had built, or at least helped the Tsarnaevs build, the bombs, and thus might have built more."

Federal prosecutors filed the 29-page motion Wednesday in U.S. District Court to ask a judge to reject Dzhokhar Tsarnaev’s request to suppress statements he made to FBI agents at the hospital following his capture last year.

During those interviews, court documents allege, Tsarnaev "readily admitted involvement" in the bombings and remained "responsive, coherent, and clearheaded" throughout the questioning.

—Becky Bratu and M. Alex Johnson