The officials, speaking on condition of anonymity because they were not authorized to discuss the ongoing investigation, say investigators recovered a 9 mm handgun believed to have been used by Tsarnaev's brother, Tamerlan, from the site of a gun battle Thursday night, which injured a Massachusetts Bay Transportation Authority officer.
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Dzhokhar Tsarnaev was believed to have been shot before he escaped a shootout with police that left his 26-year-old brother dead.
The officials tell The Associated Press that no gun was found in the boat. Boston Police Commissioner Ed Davis said earlier that shots were fired from inside the boat.
Dzhokhar Tsarnaev could face the death penalty after being charged Monday with joining forces with his brother in setting off shrapnel-packed pressure-cooker bombs near the finish line of the Boston Marathon. Three people were killed and over 260 injured. About 50 were still hospitalized.
Questions over tracking
Meanwhile on Wednesday, lawmakers asked tough questions about how the U.S. government tracked Tamerlan Tsarnaev when he travelled to Russia last year, renewing criticism from after the Sept. 11 attacks that failure to share intelligence may have contributed to last week's deadly assault.
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Following a closed-door briefing on Capitol Hill with the FBI and other law enforcement officials on Tuesday, Senator Saxby Chambliss, a Republican from Georgia and vice-chairman of the Senate Intelligence Committee, said it doesn't appear yet that anyone "dropped the ball."
But he said he was asking all the federal agencies for more information about who knew what about the suspect.
"There still seem to be serious problems with sharing information, including critical investigative information ... not only among agencies but also within the same agency in one case," said committee member Republican Senator Susan Collins of Maine.
While family said that the older Tsarnaev had been influenced by a Muslim convert to follow a strict type of Islam, 19-year-old Dzhokhar Tsarnaev remained hospitalized after days of questioning over his role in the attacks.
Conflicting stories appeared to emerge about which agencies knew about Tamerlan Tsarnaev's six-month trip to Russia last year how they handled it. Homeland Security Secretary Janet Napolitano told the Senate Judiciary Committee on immigration legislation that her agency knew about Tsarnaev's journey to his homeland.
But Senator Lindsey Graham, a South Carolina Republican, said the FBI "told me they had no knowledge of him leaving or coming back."
Information-sharing failures between agencies prompted an overhaul of the U.S. intelligence system after the Sept. 11, 2001, attacks.
Evidence suspect embraced radicalism
Meanwhile, evidence mounted that Tsarnaev had embraced a radical, anti-American strain of Islam. Family members blamed the influence of a Muslim convert, known only to the family as Misha, for steering him toward a strict type of Islam.
"Somehow, he just took his brain," said Tamerlan's uncle, Ruslan Tsarni of Montgomery Village, Md., who recalled conversations with Tamerlan's worried father about Misha's influence.
Authorities don't believe Tsarnaev or his brother had links to terror groups. However, two U.S. officials said that Tsarnaev frequently looked at extremist websites, including Inspire magazine, an English-language online publication produced by al-Qaeda's Yemen affiliate. The magazine has endorsed lone-wolf terror attacks.
Both officials spoke on condition of anonymity because they were not authorized to discuss the investigation publicly.
Boston streets reopen
On Wednesday, the area near the Boston Marathon finish line reopened to the general public, with traffic allowed to flow all the way down Boylston Street for the first time since the bombings. Delivery trucks made their way down the street under a heavy police presence, although some stores directly affected by the blasts are still boarded up.
A sprawling line of mourners gathered at the Massachusetts Institute of Technology at midday, for a service honouring the campus police officer who authorities say was shot to death by the Boston bombing suspects.
Thousands of students, faculty and staff, law enforcement officials from across the U.S., along with Vice President Joe Biden, gathered to pay respects to Sean Collier.
"He is the one of the nicest people that I've ever met," said Kelly Daumit, 35, of Seattle, an engineering student at MIT who had gone on hikes with Collier as part of the MIT Outing Club. "Everything people are saying about him is completely genuine; it's not because of what happened."
Biden was due to speak at the memorial, which was expected to draw about 10,000 at Briggs Field.
Funerals were held Tuesday for Collier and eight-year-old Martin Richard, a schoolboy from Boston's Dorchester neighbourhood, and the youngest of those killed by blasts near the marathon finish line. Martin's funeral was open only to family.
"The outpouring of love and support over the last week has been tremendous," the family said in a statement. "This has been the most difficult week of our lives."
The family also plans to hold a public memorial service for Martin Richard in the coming weeks.