WASHINGTON — Russian authorities contacted the US government with concerns about Tamerlan Tsarnaev not once but “multiple’’ times, including an alert it sent after he was first investigated by FBI agents in Boston, raising new questions about whether the FBI should have paid more attention to the suspected Boston Marathon bomber, US senators briefed on the investigation said Tuesday.

The FBI has previously said it interviewed Tsarnaev in early 2011 after it was initially contacted by the Russians. In their review, completed in summer 2011, the bureau found no evidence that Tsarnaev was a threat. “The FBI requested but did not receive more specific or additional information from’’ Russia, the agency said last week.


Following a closed briefing of the Senate Intelligence Committee Tuesday, Senator Richard Burr, a North Carolina Republican, said he believed that Russia alerted the United States about Tsarnaev in “multiple contacts,’’ including at least once since October 2011.

The details came amid revelations that the brothers may have planned to escape to New York last week with a car full of bombs, according to a senior law enforcement official. “We just killed a cop. We blew up the Marathon. And now we’re going to New York. Don’t [expletive] with us,’’ Tamerlan told a witness, the official said.

Tsarnaev’s younger brother and alleged coconspirator, Dzhokhar Tsarnaev, told authorities Sunday that the siblings carried out the deadly attack on the city’s signature road race, in part because of Tamerlan’s anger over US wars in Iraq and Afghanistan, said the law enforcement official.

The official said Dzhokhar Tsarnaev made the admission to FBI agents who interviewed him at Beth Israel Deaconess Medical Center, where he is being treated for multiple gunshot wounds. At the time, he had not yet been read his rights. The 19-year-old was listed in fair condition Tuesday, an improvement from serious condition the day before.


The alleged terrorist also told investigators that 26-year-old Tamerlan, killed Friday in a police shootout in Watertown, had been radicalized in an extreme form of Islam and that the brothers acted alone in the attack, according to the official.

The youngest person killed in the bombing, 8-year-old Martin Richard of Dorchester, was remembered in a private funeral ceremony Tuesday morning. “We laid our son Martin to rest, and he is now at peace,’’ his parents, Bill and Denise Richard, said in a brief statement. They plan to hold a public memorial service in the coming weeks.

In Stoneham, a private funeral service was held at St. Patrick Church for MIT police Officer Sean Collier, whom the Tsarnaev brothers allegedly assassinated Thursday night. Vice President Joe Biden is expected to attend a memorial Wednesday for the slain officer.

Boston’s Back Bay, shut down for more than a week after the explosions, began to reopen, as authorities led residents and business owners to their properties, many of which seemed frozen in time, with open bottles of wine still standing at restaurants hastily evacuated after the blasts.

Authorities believe that the Tsarnaev brothers planted the pair of bombs that exploded 12 seconds apart on April 15 on crowded Boylston Street. Three people died and 264 were injured, many seriously, according to the latest tally.

The US Department of Justice charged Dzhokhar Tsarnaev Monday with using a weapon of mass destruction to kill, an offense that can carry a penalty of death.

More charges will probably be added: On Thursday night and Friday morning, the brothers allegedly killed Collier, carjacked a motorist in Allston, and exchanged gunfire and hurled bombs during a firefight with officers in Watertown.


Tsarnaev’s attorneys are almost certain to challenge the legal admissibility of the admissions Tsarnaev made Sunday about the attacks and its motives.

But a senior police official said authorities have a strong witness in the case who can provide much of the same information: the man who was allegedly carjacked and abducted by the Tsarnaev brothers last Thursday night. The alleged carjacking came a few hours after the FBI released images taken from security cameras on Boylston Street, which showed two suspects carrying backpacks believed to have carried the bombs.

A law enforcement official said the carjack victim has told police that the brothers pointed guns at him and admitted to the bombing in an apparent effort to intimidate him. The brothers allegedly forced the man to turn over his ATM card and password.

By the time officers confronted the brothers early Friday morning, “we already knew these guys had admitted to killing three civilians and a police officer and that they were prepared to kill many others,’’ the senior official said.

The official said the bombers repeatedly told the victim they were going to New York. Investigators are trying to determine if the brothers had friends or coconspirators there. But their haphazard, ill-planned escape has many investigators skeptical that there were other radicals involved in the attack.

“If they had accomplices in New York, you’d think they would have had an established contingency plan to get down there to them and wouldn’t be shooting cops and carjacking cars to steal ATM cards to finance their escape,’’ the official said. “That said, we haven’t ruled out anything in New York. We’re looking into who they knew down there and was anyone in New York prepared to hide them.’’

New information also emerged Tuesday on the suspects’ interest in explosives.

Tamerlan Tsarnaev, the elder brother, bought large mortar kits in February from a New Hampshire fireworks store less than an hour’s drive from Boston, said Phantom Fireworks vice president William Weimer. According to store records, Tsarnaev spent $200 for two “Lock and Load’’ kits, each with 24 shells, from the Phantom Fireworks store in Seabrook, N.H., Weimer said.

The shells contain a mix of clay, a powder to deliver color and noise, and two powdered explosives. He said only a negligible amount of explosives could be extracted from all 48 shells. “What my guess is, they purchased these products in early February, experimented with them, and probably came to the conclusion that they couldn’t harvest enough powder to do what they wanted to do with them,’’ Weimer said.

The lawyer for Tamerlan Tsarnaev’s widow issued a statement on her behalf Tuesday, saying Katherine Russell knew nothing of the bombing plot. “The injuries and loss of life — to people who came to celebrate a race and a holiday — has caused profound distress and sorrow to Katie and her family. The reports of involvement by her husband and brother-in-law came as an absolute shock to them all.’’

In Washington, senators said the closed-door briefing on Tuesday also revealed failures among federal agencies to share vital information about Tsarnaev, indicating, they said, that the US government still has not established a strong system to “connect the dots’’ about would-be terrorists residing in the United States more than a decade after 9/11.

Senator Susan Collins, a Maine Republican and a member of the Senate Intelligence Committee, praised law enforcement authorities for quickly putting a halt to the violent spree Thursday night and Friday. “But I’m very concerned that there still seem to be serious problems with the sharing of information, including critical investigative information,’’ she said after emerging from the briefing. “That is troubling to me, this many years after the attacks on our country in 2001, that we still seem to have stovepipes that prevent information from being shared effectively.’’

Burr, the North Carolina senator, contended that the Russians contacted the FBI several times, but the bureau disputed that assertion.

Spokesman Paul Besson said late Tuesday that the FBI maintains that it had only one contact with the Russians about Tsarnaev, in spring 2011, but could not comment about other agencies.

Warnings raised by Russia have loomed large in the investigation of how Tsarnaev, a Kyrgyzstan national, and his younger brother, Dzhokhar, a naturalized US citizen, allegedly prepared for the bombing.

“I think the increasing signals are that these are individuals that were radicalized, especially the older brother, over a period of time,’’ Senator Marco Rubio, Republican of Florida, said after the briefing. He said the brothers “used Internet sources to gain not just the philosophical beliefs that radicalized them, but also learning components of how to do these sorts of things.’’

US officials have faced tough questions for not tracking the older brother’s travels to the Russian provinces of Dagestan and Chechnya, where he spent more than half of 2012 and may have interacted with militant groups or individuals.

Senator Lindsey Graham, Republican of South Carolina, said Monday that the FBI told him it was not aware of the older Tsarnaev’s travels because his name had been misspelled on an airliner passenger list. US Secretary of Homeland Security Janet Napolitano confirmed the misspelling during a hearing before the Senate Judiciary Committee Tuesday, but she said Homeland Security nonetheless was aware of his trip.

“Even with the misspelling under our current system, there are redundancies, and so the system did ping when he was leaving the United States,’’ she said.

Her disclosure that Homeland Security knew of the trip raised questions among lawmakers. “I want to make sure that DHS is talking to the FBI,’’ said Senator Charles Grassley, the ranking Republican on the Judiciary Committee. “It looks to me like there is a lack of communication.’’