(CNN) -- The surviving suspect in the Boston Marathon bombings has cited the U.S. wars in Afghanistan and Iraq as motivating factors behind last week's attack, a U.S. government official said Tuesday.
Dzhokhar Tsarnaev has been able to communicate with investigators in a limited fashion from his hospital bed and told them that neither he nor his brother Tamerlan, now dead, had any contact with terrorist groups overseas. The official cautioned that the interviews were preliminary, however, and that Tsarnaev's account needs to be checked out.
The 19-year-old has told investigators the brothers were self-radicalized via the Internet. Investigators also are looking into whether the online English-language magazine Inspire, put out by Al Qaeda in the Arabian Peninsula, was used for instruction on how to make the bombs, but another source cautioned that other outlets could have provided that information.
The twin blasts just before the finish line of the April 15 race killed three people and wounded more than 260 and turned a chunk of downtown Boston into a crime scene, disrupting the normal routines of countless others.
Authorities slowly began allowing residents and business owners back into the area Tuesday. There was no word on when the street where the bombings occurred will be fully open to the public. That, the city says, will depend on how quickly building owners can make repairs and other issues.
But the staged opening is the latest sign that Boston is working to return to normal after an extraordinary week that began with the bombings and ended with a dramatic manhunt that all but locked down the nation's fifth largest metro area for the better part of a day.
Business owner Ed Borash was among those who returned Tuesday. He said he and his son narrowly missed injury in the bombing.
"I've had a tough time," he said. "It's just one of those things. It's very emotional."
Helena Collins, a businessperson in the area, said it was important to get up and running again, but not just for economic reasons.
"For us and our business, it's really about how do we get back to Boston, how do we band together, how do we help those that were seriously injured that are going to have lifelong struggles," she said.
Also Tuesday, candidates for the state's vacant U.S. Senate seat resumed their campaigns, which had been suspended in the wake of the bombing.
Meanwhile, two victims of the bombing were being laid to rest.
Family members of 8-year-old Martin Richard held a private funeral Mass Tuesday, his parents said in a statement. A public memorial service is planned, they said.
"The outpouring of love and support over the last week has been tremendous," Denise and Bill Richard said in the statement. "We laid our son Martin to rest, and he is now at peace."
Slain Massachusetts Institute of Technology police Officer Sean Collier was to be buried later Tuesday after a private memorial service in Stoneham, Massachusetts, CNN affiliate WHDH reported.
A memorial service open to law enforcement officers and the MIT community is scheduled for Wednesday on MIT's campus, the university said.
New details on officer's slaying
Collier was killed Thursday night, near the beginning of a wild 24 hours that culminated in Dzhokhar Tsarnaev's capture in the backyard of a home in Watertown, a Boston suburb. Authorities suspect Tsarnaev and his 26-year-old brother of killing the officer, though Dzhokhar Tsarnaev has not been charged in Collier's death.
According to a source with direct knowledge of the investigation, Collier didn't even have time to activate his emergency alert before being shot four or five times in the chest and head as he sat in his patrol car on the MIT campus.
It's not clear why the brothers allegedly ambushed the officer, the source said.
The source said investigators believe the Tsarnaevs then carjacked a black SUV, took the driver hostage and drove past the scene of the shooting before going to a gas station.
Carjacking victim speaks
In an exclusive interview with CNN affiliate WMUR, a man identifying himself as the carjacking victim said he was worried for his life.
"They asked me where I'm from. I told them I'm Chinese," WMUR quoted the man as saying. "I was very scared. I asked them if they were going to hurt me. They said they won't hurt me. I was thinking, 'I think they will kill me later.' "
The man escaped when the brothers stopped to fill up the gas tank, running for his life as one of the brothers swore at him, WMUR reported.
Soon after, the brothers encountered police, setting off a furious gun battle in which authorities say they fired handguns and hurled explosives at pursuing officers before Tamerlan Tsarnaev was shot. As the younger brother fled in the vehicle, he apparently ran over Tamerlan, authorities said.
Tamerlan Tsarnaev was pronounced dead early Friday. On Friday night, police captured Dzhokhar Tsarnaev hiding inside a boat that was trailered in a backyard.
In a statement issued through their lawyers Tuesday, the suspects' sisters -- Ailina and Bella Tsarnaev -- said they were saddened "to see so many innocent people hurt after such a callous act."
"As a family, we are absolutely devastated by the sense of loss and sorrow this has caused," they said. "We don't have any answers but we look forward to a thorough investigation and hope to learn more."
And Tamerlan Tsarnaev's wife, Katherine Russell, issued a statement through her attorney's office saying she is "doing everything she can to assist with the investigation" and said she and her family are shocked and distraught.
"The reports of involvement by her husband and brother-in-law came as an absolute shock to them all," the statement said.
The Tsarnaev family is from the Russian republic of Chechnya and fled the brutal wars there in the 1990s. The two brothers were born in Kyrgyzstan; Dzhokhar became a U.S. citizen in 2012. His brother was a legal U.S. resident.
Although Tamerlan Tsarnaev had become increasingly radical in the past three or four years, there was no evidence Monday that he had any active association with international jihadist groups. But Dzhokhar Tsarnaev conveyed to authorities that his brother believed Islam is under attack and its adherents must fight back, a U.S. government source said Monday.
Communicating with investigators by writing and nodding, Dzhokhar Tsarnaev has indicated that his older brother masterminded the bombings, the source said.
The younger Tsarnaev has been charged with using and conspiring to use a weapon of mass destruction resulting in death, as well as one count of malicious destruction of property by means of an explosive device resulting in death.
Although Tsarnaev is heavily sedated and on a ventilator at Beth Israel Deaconess Medical Center, he was "alert, mentally competent and lucid" during a brief initial court appearance at his bedside Monday, U.S. Magistrate Judge Marianne Bowler found.
Tsarnaev was shot in the head, neck, legs and one hand, according to an FBI affidavit supporting the charges. It's not clear whether he was wounded during his capture Friday night or in the earlier shootout with police.
An FBI official said agents interviewed Tamerlan Tsarnaev in 2011 at the request of the Russian government. The FBI said Russia claimed that he was a follower of radical Islam and that he had changed drastically since 2010.
But the Russian government's request was vague, a U.S. official and a law enforcement source said Sunday. The lack of specifics limited how much the FBI was able to investigate Tamerlan, the law enforcement official said.
Suspects' mother reacts
The suspects' mother, Zubeidat Tsarnaev, said Tuesday that she believed her sons had been framed.
Speaking from her home in Dagestan -- a Russian republic on the Caspian Sea -- Tsarnaev said she thinks her older son died because he was a Muslim and charged that authorities silenced her younger son to prevent him from defending himself.
She said family members have arranged for Tamerlan Tsarnaev to be buried at a mosque in Cambridge, Massachusetts, Tuesday or Wednesday.
An official with the Islamic Society of Boston said it has not received any funeral requests from the family. A spokesman for the chief medical examiner's office also said officials there have heard nothing about plans by the slain suspect's family to claim his body.AlertMe