"It was a remote control for toy cars," US Representative Dutch Ruppersberger, the top Democrat on the House Intelligence Committee, told reporters after officials from the Department of Homeland Security, FBI and National Center for Counterterrorism briefed the committee.
"Which says to me, and brother number two has said, they got the information on how to build the bomb from Inspire magazine," Ruppersberger added.
Inspire was created by the American-Yemeni preacher Anwar al-Awlaki, a leader of al Qaeda's affiliate in Yemen who was killed in a US drone strike.
Ruppersberger said the article on bomb-building in Inspire was headlined: "How to build a bomb in your mom's kitchen."
Police say two brothers, Tamerlan and Dzhokhar Tsarnaev, planted and detonated two pressure-cooker bombs near the finish line of the Boston Marathon on April 15.
Tamerlan Tsarnaev, 26, was killed in a shootout with police. Dzhokhar Tsarnaev, 19, lies wounded in a Boston hospital and has been providing some information to authorities.
Ruppersberger also confirmed that at least some of the explosives used in the attack had come from a fireworks shop in New Hampshire.
"One of the brothers, the oldest brother, went to a shop in New Hampshire ... and asked for the most volatile explosives, so that you'd 'get the best bang,'" Ruppersberger said.