WASHINGTON — The chairman of the House Homeland Security Committee said Sunday that the FBI is investigating in the United States and overseas to determine whether the suspects in the Boston Marathon bombing received training that helped them carry out the attack.

Dzhokhar Tsarnaev, 19, is charged with joining with his older brother, Tamerlan, who’s now dead, in setting off the shrapnel-packed pressure-cooker bombs. The bombs were triggered by a remote detonator of the kind used in remote-control toys, U.S. officials have said.

U.S. officials investigating the bombings have said that so far there is no evidence of a wider plot, including training, direction or funding for the attacks.

A criminal complaint outlining federal charges against Dzhokhar Tsarnaev described him as holding a cellphone in his hand minutes before the first explosion. The brothers are ethnic Chechens from Russia who came to the U.S. about a decade ago with their parents.

“I think given the level of sophistication of this device, the fact that the pressure cooker is a signature device that goes back to Pakistan, Afghanistan, leads me to believe — and the way they handled these devices and the tradecraft — ... that there was a trainer and the question is where is that trainer or trainers,” said Rep. Michael McCaul, R-Texas, on “Fox News Sunday.”

Rep. Adam Schiff, D-Calif., of the House Intelligence Committee, said he thought it’s “probably true” that the attack was not linked to a major group. But, he told CNN’s “State of the Union,” that there “may have been radicalizing influences” in the U.S. or abroad. “It does look like a lot of radicalization was self-radicalization online, but we don’t know the full answers yet.”

On ABC’s “This Week,” moderator George Stephanopoulos raised the question to the chairman of the House Intelligence Committee about FBI suspicions that the brothers had help in getting the bombs together. “Absolutely, and not only that, but in the self-radicalization process, you still need outside affirmation,” responded Rep. Mike Rogers, R-Mich.