Tsarnaev was listed in serious but stable condition at Beth Israel Deaconess Medical Center, unable to speak because of a gunshot wound to the throat. His brother, Tamerlan, 26, died last week in a fierce gunbattle with police.
In outlining the evidence against him in court papers, the FBI said Tsarnaev was seen on surveillance cameras putting a knapsack down on the ground near the site of the second blast and then manipulating a cellphone and lifting it to his ear.
After the first explosion went off about a block down the street and spread fear through the crowd, Tsarnaev unlike nearly everyone around him looked calm and quickly walked away, the FBI said. Just 10 seconds or so later, the second blast occurred where he left the knapsack, the FBI said.
The FBI did not make it clear whether authorities believe he used his cellphone to detonate one or both of the bombs or whether he was talking to someone.
The court papers also said that during the long night of crime Thursday and Friday that led to the older brother's death and the younger one's capture, one of the Tsarnaev brothers told a carjacking victim: "Did you hear about the Boston explosion? I did that."
The brothers are ethnic Chechens from Russia who have lived in the U.S. for about a decade. Investigators are focusing on a trip the older brother made last year to Chechnya and Dagestan, in a region of Russia that has become a hotbed of separatist politics and Islamic extremism.
Tsarnaev was charged with using and conspiring to use a weapon of mass destruction against persons and property, resulting in death. He is also likely to face state charges in connection with the shooting death of an MIT police officer.
The Obama administration said it had no choice but to prosecute Tsarnaev in the federal court system. Some politicians had suggested he be tried as an enemy combatant in front of a military tribunal, where defendants are denied some of the usual U.S. constitutional protections.
But Tsarnaev is a naturalized U.S. citizen, and under U.S. law, American citizens cannot be tried by military tribunals, White House spokesman Jay Carney said. Carney said that since the Sept. 11 attacks, the federal court system has been used to convict and incarcerate hundreds of terrorists.
In its criminal complaint, the FBI said it searched Tsarnaev's dorm room at the University of Massachusetts-Dartmouth on Sunday and found BBs as well as a white hat and dark jacket that look like those worn by one of one of the suspected bombers in the surveillance photos the FBI released a few days after the attack.
Seven days after the bombings, meanwhile, Boston was bustling Monday, with runners hitting the pavement, children walking to school and enough cars clogging the streets to make the morning commute feel almost back to normal.
Residents paused in the afternoon to observe a moment of silence at 2:50 p.m., the time of the first blast. Church bells tolled across the city and state in tribute to the victims.
Also, hundreds of family and friends packed a church in Medford for the funeral of bombing victim Krystle Campbell, a 29-year-old restaurant worker. A memorial service was scheduled for Monday night at Boston University for 23-year-old Lu Lingzi, a graduate student from China.
Fifty-one victims remained hospitalized Monday, three of them in critical condition.
At the Snowden International School on Newbury Street, a high school set just a block from the bombing site, jittery parents dropped off children as teachers some of whom had run in the race greeted each other with hugs.
Carlotta Martin of Boston said that leaving her kids at school has been the hardest part of getting back to normal.
"We're right in the middle of things," Martin said outside the school as her children, 17-year-old twins and a 15-year-old, walked in, glancing at the police barricades a few yards from the school's front door.
"I'm nervous. Hopefully, this stuff is over," she continued. "I told my daughter to text me so I know everything's OK."
Tsarnaev was captured Friday night after an intense all-day manhunt that brought the Boston area to a near-standstill. He was cornered and seized, wounded and bloody, after he was discovered hiding in a tarp-covered boat in a Watertown backyard.
He had apparent gunshot wounds to the head, neck, legs and hand, the FBI said in court papers.
Sen. Dan Coats of Indiana, a member of the Senate Intelligence Committee, said Sunday that Tsarnaev's throat wound raised questions about when he will be able to talk again, if ever. It was not clear whether the wound was inflicted by police or was self-inflicted.
The wound "doesn't mean he can't communicate, but right now I think he's in a condition where we can't get any information from him at all," Coats told ABC's "This Week."
Federal authorities have asked to speak with the wife of Tamerlan Tsarnaev, and her lawyer said he is discussing with them how to proceed.
Amato DeLuca told The Associated Press on Sunday that Katherine Russell Tsarnaev did not speak to federal officials who came to her parents' home in North Kingstown, R.I., Sunday evening, where she has been staying since her husband was killed during a getaway attempt early Friday.
DeLuca said he spoke with the officials instead, but would not offer further details.
"I spoke to them, and that's all I can say right now," he said. "We're deciding what we want to do and how we want to approach this."
On Monday morning, Katherine Tsarnaev was seen leaving her house, in a car driven by her mother and escorted by two unmarked cars. Multiple news outlets reported she went to her lawyer's office. She returned home shortly after 1 p.m., again escorted by unmarked cars.
Her lawyer did not immediately return messages left Monday.
DeLuca also offered new details on Tamerlan Tsarnaev's movements in the days after the bombings, saying the last day he was alive that "he was home" when his wife left for work. When asked whether anything seemed amiss to his wife following the bombings, DeLuca responded, "Not as far as I know." He said she learned her husband was a suspect in the bombings by seeing it on TV. He would not elaborate.
DeLuca said his client did not suspect her husband of anything, and that there was no reason for her to have suspected him. He said she had been working 70 to 80 hours, seven days a week as a home health care aide. While she was at work, her husband cared for their toddler daughter, DeLuca said.
"When this allegedly was going on, she was working, and had been working all week to support her family," he told the AP.
He said Dzhokhar Tsarnaev was off at college and she saw him "not at all" at the apartment they shared with her mother-in-law.
Katherine Russell Tsarnaev was attending Suffolk University in Boston when friends introduced her to her future husband at a nightclub, DeLuca said. They dated on and off, then married in 2009 or 2010, he said.
She was raised Christian, but at some point after meeting Tamerlan Tsarnaev, she converted to Islam, he said. When asked why she converted, he replied: "She believes in the tenets of Islam and of the Koran. She believes in God."
Doctors: All Boston bomb patients likely to live
One week after the Boston Marathon bombings, doctors say everyone injured in the blasts who made it alive to a hospital now seems likely to survive.
More than 180 people were hurt in the explosions, and at least 14 of them lost all or part of a limb. As of Monday, 51 remained hospitalized. Three are listed as critical and five are in serious condition. Among the critical is transit system police officer who nearly bled to death in a shootout with the bombing suspects. Doctors say he is expected to recover.
The three people who died in the blasts died at the scene, as did another officer who was shot.
Senator says dead Boston suspect's name misspelled
A Republican senator says the name of Tamerlan Tsarnaev the suspect in the Boston Marathon bombing who died in a firefight with police was misspelled on his 2011 trip to Russia.
Sen. Lindsey Graham of South Carolina said Tsarnaev's correct name never went into "the system," and this thwarted the FBI in discovering the six-month trip. Graham said on Fox News that he spoke to the assistant director of the FBI on Sunday night.
Graham's spokesman, Kevin Bishop, confirmed the senator's comments on Monday.
The trip is the subject of the investigation into last Monday's deadly bombings.
Rep. Mike Rogers, chairman of the House intelligence committee, had said Sunday that Tsarnaev may have used an alias to travel to Russia. Rogers made the comments on NBC. Aunt: Boston bombings suspect struggled with Islam
MAKHACHKALA, Russia • The elder suspect in the Boston bombings regularly attended a mosque and spent time learning to read the Quran, but he struggled to fit in during a trip to his ancestral homeland in southern Russia last year, his aunt said.
Tamerlan Tsarnaev seemed more American than Chechen and "did not fit into the Muslim life" in Russia's Caucasus, Patimat Suleimanova told The Associated Press. She said when Tsarnaev arrived in January 2012, he wore a winter hat with a little pompom, something no local man would wear, and "we made him take it off."
Tsarnaev and his younger brother are accused of setting off the two bombs at the Boston Marathon on April 15 that killed three people and wounded more than 180. Tsarnaev, 26, was killed in a gun battle with police. His 19-year-old brother, Dzhokhar Tsarnaev, was later captured alive, but badly wounded.
Investigators are focusing on the six months Tsarnaev spent last year in the predominantly Muslim provinces of Dagestan and Chechnya to see if he was radicalized by the militants in the area who have waged a low-level insurgency against Russian security forces for years.
The Tsarnaev family moved to the United States a decade ago, but the suspects' parents are currently in Russia. Their father said he hopes to go to the United States this week to seek "justice and the truth."
Suleimanova, who wore a pea-green headscarf, said her nephew prayed regularly and studied the Muslim holy book. "He needed this. This was a necessity for him," she said.
Every day, using Skype, he spoke to his American-born wife, who had recently converted to Islam, and at times she instructed him on how to observe religious practices correctly when he lapsed, Suleimanova said Sunday from her home in Makhachkala, the capital of Dagestan. She said her nephew was considering bringing his wife to Dagestan.
His parents insist he spent much of his time visiting relatives in his mother's and father's extended families in Dagestan and Chechnya, but details of his whereabouts are vague and contradictory. His father says Tsarnaev stayed with him in Makhachkala, regularly sleeping late.
His aunt, however, said neither of Tsarnaev's parents was in Russia when he arrived. One reason his father came last year, Suleimanova said, was to make sure his elder son returned to the United States. It was not clear when his father or mother arrived. His mother was arrested in the U.S. in June on charges of shoplifting.
Tsarnaev's father explained his son's trip by saying he needed to get a new Russian passport. But an official with the federal migration service in Dagestan said Monday that Tsarnaev had applied for a new passport in July, but never picked it up, the Interfax news agency reported. Tsarnaev returned to the U.S. on July 17.
His mother, Zubeidat Tsarnaeva, told the AP that her son greatly enjoyed his time with her relatives, but never traveled to her native village in a mountainous region of Dagestan, which is a hotbed of an ultraconservative strain of Islam known as Wahabbism. Wahabbism was introduced to the Caucasus in the 1990s by preachers and teachers from Saudi Arabia.
The mother said her relatives now all live in Makhachkala and the town of Kaspiisk. She refused to say which mosque her son frequented, but Tsarnaev's parents and aunt firmly denied that he met with militants or fell under the sway of religious extremists.
"He used to say, 'I want to go somewhere in the mountains, to be all by myself, to escape from everyday life, to be alone,'" Suleimanova said.
The suspects' father, Anzor Tsarnaev, said he intends to travel to the U.S. "I want normal justice," he said. "I have many questions for the police. You know, I am a lawyer myself and I want to clear up many things. .... I want justice and the truth."
The family said he wants to bring Tsarnaev's body back to Russia.
The Associated Press