Tsarnaev Dzhokhar Tsarnaev, 19, suspect No. 2 in the Boston Marathon explosion, is pictured in this undated FBI handout photo. Photo: Reuters/FBI

What do Christmas lights, model cars and fireworks have in common? The Tsarnaev brothers found a way to combine them to make the pressure cooker bombs that they donated at the 2013 Boston Marathon finish line, according to court documents obtained by CNN.

Accused bombers Dzhokhar and Tamerlan Tsarnaev used Christmas lights for bomb fuses and model car parts for remote-control detonators, federal prosecutors said in a motion filed Wednesday. And the fireworks were used for their explosive powder. The brothers reportedly crushed hundreds of fireworks and emptied them for their powder.

"These relatively sophisticated devices would have been difficult for the Tsarnaevs to fabricate successfully without training or assistance from others," the motion stated.  

The 2013 bombing killed four people and injured more than 200. Dzhokhar pleaded not guilty in court last July and Tamerlan was killed after the bombing during a massive manhunt.