New York - The twin bombs that went off at the Boston Marathon last year were made using improvised fuses from Christmas lights and detonators constructed from model car parts, US prosecutors said.
The 15 April, 2013 attack at the renowned race killed three people and injured 264 others, many of them badly maimed by a rain of shrapnel.
The blasts were allegedly planned and carried out by two brothers, Tamerlan and Dzhokhar Tsarnaev.
Tamerlan was shot dead by police on 19 April, 2013, after killing an officer and Dzhokhar was captured and stands accused of 30 federal charges. He is awaiting trial and could face the death penalty if convicted.
In documents filed on Wednesday, prosecutors specify that the two pressure-cooker bombs used in the attack were "constructed using improvised fuses made from Christmas lights and improvised, remote-control detonators fashioned from model car parts".
The documents were filed in response to a motion by the defence to suppress statements suspect Dzhokhar Tsarnaev made while hospitalised the day after his arrest - before he had been informed of his rights.
The prosecutors state that "facts known to law enforcement at the time they interviewed Tsarnaev provided reason to believe that the Tsarnaevs had accomplices and that they or others might have built additional bombs that posed a continuing danger to public safety".
They also say that the first interview of Tsarnaev by FBI agents started "nearly 24 hours" after he was hospitalised and that he had confirmed to them that he could hear and respond to them - despite his tracheotomy - and that he was not in too much pain.
"From the moment the agents began questioning Tsarnaev about the marathon bombings, he readily admitted his own involvement," they said.
"But Tsarnaev steadfastly denied that any other bombs existed or that anyone else was involved in the bombings."
The prosecutors specify that before hiding in the boat in which he was ultimately found following a massive manhunt, the younger Tsarnaev also "smashed" both of his cell phones to avoid being detected via the devices, they said.
Earlier this month, lawyers for Tsarnaev asked a US court to rule out capital punishment for their client - a request prosecutors opposed in a separate document.