Investigators Dig for Roots of Bomb Suspects’ Radicalization

The two men suspected in the Boston Marathon bombings were armed with a small arsenal of guns, ammunition and explosives when they first confronted the police early Friday, and were most likely planning more attacks, the authorities said Sunday.

United States officials said they were increasingly certain that the two suspects had acted on their own, but were looking for any hints that someone had trained or inspired them. The F.B.I. is broadening its global investigation in search of a motive and pressing the Russian government for more details about a Russian request to the F.B.I. in 2011 about one of the suspects’ possible links to extremist groups, a senior United States official said Sunday.

Among the unanswered questions facing investigators are where the suspects acquired their weapons and explosives, how they got the money to pay for them, and whether others helped plan and carry out the attack last Monday.  Mayor Thomas M. Menino of Boston said he believed the brothers were not affiliated with a larger network.  “All of the information that I have, they acted alone, these two individuals, the brothers,” he said on ABC News’s “This Week.”

Mr. Menino said Tamerlan had “brainwashed” his younger brother to follow him and “read those magazines that were published on how to create bombs, how to disrupt the general public, and things like that.”

Tamerlan Tsarnaev was an amateur boxer who had hoped to fight on the U.S. Olympic team, a man who said he had no American friends. Dzhokhar Tsarnaev wrestled at a prestigious high school, won a scholarship from his city and went on to university.  He identified himself then as a Muslim and said he did not drink or smoke: “God said no alcohol.” He said he hoped to fight for the U.S. Olympic team and become a naturalized American. He said he was studying to become an engineer.

They had come to the United States about 10 years ago from a Russian region near Chechnya, according to an uncle, Ruslan Tsarni of Montgomery Village, Md. They had two sisters. As kids they rode bikes and skateboards on quiet Norfolk Street in Cambridge, Mass.

But their lives appeared to take different turns — at least until this week, when a video caught them together on Boylston Street, moments before two bombs unleashed terror at the finish line of America’s most famous race.

The suspects’ uncle Ruslan Tsarni, said in an interview on Sunday that he had first noticed a change in the older brother in 2009. Mr. Tsarni sought advice from a family friend, who told him that Tamerlan’s radicalization had begun after he met a recent convert to Islam in the Boston area. Mr. Tsarni said he had later learned from a relative that his nephew had met the convert in 2007.

As scrutiny increased on how the brothers had been radicalized, Representative Michael McCaul, a Texas Republican who heads the Homeland Security Committee, and Representative Peter T. King, a New York Republican on the panel, sent a letter to the directors of three of the nation’s leading intelligence-gathering agencies calling the F.B.I.’s handling of the case “an intelligence failure.”

Their efforts included analyzing records from the brothers’ phones and computers, to find associates and witnesses and extremist group affiliations. The agents also scoured credit card records and other material seized from their apartment and car for evidence of bomb components, the backpacks used or any other evidence that could tie them to the bombings.