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.