In an appearance on "Fox News Sunday," the chairman of the House Homeland Security Committee said most experts agree someone trained Tamerlan and Dzhokhar Tsarnaev to make the pressure cooker bombs that killed three people and injured 260 others April 15.
The FBI revealed toy remote-controllers were used to detonate the two bombs at the site of the Boston Marathon. The controllers appeared to be more sophisticated than what is found on the al-Qaida-linked online magazine Dzhokhar said he and his brother used to learn how to make bombs, Fox reported.
"I think given the level of sophistication of this device, the fact that the pressure cooker is a signature device, goes back to Pakistan or Afghanistan ... and the way they handled these devices and the tradecraft leads me to believe that there was a trainer. And the question is, where is that trainer or trainers? Are they overseas in the Chechen region or are they in the United States?" McCaul said.
He said he is concerned there may have been a wider conspiracy.
Sen. Joe Manchin III, D-W.Va., also appearing on the show, said he also believes there's a foreign connection to the incident.
"As Mike has said ... the sophisticated bomb they made and how they detonated it and things of this sort ... I think they were a little bit more advanced than what the [al-Qaida] website would have allowed a person to be," he said.
"And also [Tamerlan's] six months overseas, coming back, and then the Russians intervening, and Russians warning us. Did they tell us all they knew? Why did they withhold information? There needs to be a tremendous follow-up on this thing, and better coordination," Manchin added.