A law enforcement official told CNN Thursday that at least one of the two bombs -- the second to explode -- was detonated by remote control. Rep. Dutch Ruppersberger, a Maryland Democrat and member of the House Select Committee on Intelligence, said that the brothers used a remote control device similar to those used to guide toy cars.
While video taken near the scene of the explosions shows Dzhokhar Tsarnaev talking on a cell phone, it is not known whether he used it to trigger a device, a law enforcement official said.
Those twin blasts killed three people and injured more than 260 others, 14 of whom had limbs amputated. As of Thursday evening, 34 of those wounded were still being treated at Boston hospitals, including one patient in critical condition.
The manhunt for those responsible ended last Friday, when Dzhokhar Tsarnaev was captured after a tense standoff after he'd hidden in a boat in the yard of a home in the Boston suburb of Watertown, Massachusetts.
The teenager was unarmed when he was wounded in a barrage of gunfire, and there was no firearm found in the boat, said several sources from difference agencies familiar with the investigation.
Authorities previously said in a criminal complaint that there was a standoff involving gunfire before Dzhokhar's capture. Watertown Police Chief Edward Deveau told CNN's Wolf Blitzer on Saturday that it was his understanding that the suspect fired from the boat.
This came after Tsarnaev and his older brother allegedly shot and killed Massachusetts Institute of Technology campus police officer Sean Collier in Cambridge.
The Middlesex County District Attorney's Office hopes to bring charges against Dzhokhar Tsarnaev for his alleged role in incidents last week in Cambridge and Watertown, spokeswoman Stephanie Guyotte said Thursday.