Tsarnaevs used Christmas lights to make bomb fuses

The accused Boston marathon bombers used Christmas lights and model-car parts to make the explosives, prosecutors said in court documents obtained by CNN Wednesday.

"The Marathon bombs were constructed using improvised fuses made from Christmas lights and improvised, remote-control detonators fashioned from model car parts," federal prosecutors said in a motion filed Wednesday. "These relatively sophisticated devices would have been difficult for the Tsarnaevs to fabricate successfully without training or assistance from others."

To obtain explosive fuel for the bombs, the filing says, Dzhokhar and Tamerlan Tsarnaev "appeared to have crushed and emptied hundreds of individual fireworks containing black powder."

CNN first learned of the new court documents on Twitter.

Dzhokhar Tsarnaev, 20, is accused of planting the bombs at the finish line of the 2013 race, along with Tamerlan, who was killed during the manhunt that paralyzed Boston. He has pleaded not guilty to killing four people and wounding more than 200.