Amerikanske folkevalgte i kontakt med FBI sier de tror Tsarnajev-brødrene fikk opplæring i bruk av trykkoker-bomber. Utføringen var såpass sofistikert at de neppe har funnet ut av det på egen hånd.

Men så langt er det ikke noe som indikerer at de var medlem av noen gruppe.

“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.”

“Are they overseas in the Chechen region or are they in the United States?” McCaul said. “In my conversations with the FBI, that’s the big question. They’ve casted a wide net both overseas and in the United States to find out where this person is. But I think the experts all agree that there is someone who did train these two individuals.”

Rep. Adam Schiff, D-Calif., a member 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.

“We still have persons of interest that we’re working to find and identify and have conversations with,” he added.

At this point in the investigation, however, Sen. Claire McCaskill said there was no evidence that the brothers “were part of a larger organization, that they were, in fact, part of some kind of terror cell or any kind of direction.”

The Missouri Democrat, who’s on the Senate Homeland Security and Governmental Affairs Committee, told CBS’ “Face the Nation” that “it appears, at this point, based on the evidence, that it’s the two of them.”

Homemade bombs built from pressure cookers have been a frequent weapon of militants in Afghanistan, India and Pakistan. Al-Qaeda’s branch in Yemen once published an online manual on how to make one.

Tamerlan Tsarnaev was an ardent reader of jihadist websites and extremist propaganda, officials have said. He frequently looked at extremist sites, including Inspire magazine, an English-language online publication produced by al-Qaeda’s Yemen affiliate.