The two brothers suspected of bombing the Boston Marathon appear to have been motivated by their religious faith but do not seem connected to any Muslim terrorist groups, U.S. officials said Monday after interrogating the severely wounded younger man. He was charged with federal crimes that could bring the death penalty.

Dzhokhar Tsarnaev, 19, was charged in his hospital room with using a weapon of mass destruction to kill. He was accused of joining with his older brother, Tamerlan _ now dead _ in setting off the pressure-cooker bombs that killed three people and wounded more than 200 a week ago.

The brothers, ethnic Chechens from southern Russia who had been living in the U.S. for about a decade, practiced Islam.

Two U.S. officials said preliminary evidence from an interrogation suggests the brothers were motivated by religion but were apparently not tied to any Islamic terrorist organizations. The officials spoke on condition of anonymity because they were not authorized to publicly discuss the investigation.

The criminal complaint containing the charges against Dzhokhar Tsarnaev shed no light on the motive. But it gave a detailed sequence of events and cited surveillance-camera images of him dropping off a backpack with one of the bombs and using a mobile phone, perhaps to coordinate or detonate the blasts.

The Massachusetts university student was listed in serious but stable condition at Beth Israel Deaconess Medical Center with a gunshot wound to the throat and other injuries. His 26-year-old brother died last week in a fierce gunbattle with police.

“Although our investigation is ongoing, today's charges bring a successful end to a tragic week for the city of Boston and for our country,” Attorney General Eric Holder said in a statement.

The charges carry the death penalty or a prison sentence of up to life.

“He has what's coming to him,” a wounded Kaitlynn Cates said from her hospital room. She was at the finish line when the first blast knocked her off her feet, and she suffered an injury to her lower leg.

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 mobile phone and lifting it to his ear.

Seconds later, the first explosion went off about a block down the street and spread fear and confusion through the crowd. But 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 had 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.”

In addition to the federal charges, the younger Tsarnaev brother 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, 2001 attacks, the federal court system has been used to convict and imprison 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. Eastern, the time of the first blast. Church bells tolled across the city and state in tribute to the victims.

Standing on the steps of the state Capitol, Massachusetts Gov. Deval Patrick bowed his head and said after the moment of silence: “God bless the people of Massachusetts.”

On Boylston Street, where the bombing took place, the silence was broken when a Boston police officer pumped his fists in the air and the crowd erupted in applause. The crowd then quietly sang “God Bless America.”

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.

Meanwhile, investigators in the Boston suburb of Waltham are looking into whether there are links between Tamerlan Tsarnaev and an unsolved 2011 slaying. Tsarnaev was a friend of one of three men found dead in an apartment with their necks slit and their bodies reportedly covered with marijuana. (AP)