Boston bomb suspect Dzhokhar Tsarnaev on Monday was charged with using a weapon of mass destruction and could face the death penalty if convicted, the US Department of Justice said.
Tsarnaev, 19, also has been charged with one count of malicious destruction of property by means of deadly explosives, the DOJ said in a statement. He was arraigned in his hospital bed, where he remains in serious condition.
If the teen, a naturalized US citizen of Chechen descent, is convicted of the federal charges over last week's twin marathon blasts, which left three dead and 200 wounded, he could be sentenced to jail time -- or to death.
"We've once again shown that those who target innocent Americans and attempt to terrorize our cities will not escape from justice," said US Attorney General Eric Holder. A first court hearing was set for May 30.
The unsealing of the federal charges against Tsarnaev, who suffered a gunshot wound to the throat after being captured late Friday, came as White House spokesman Jay Carney said he would not be deemed an "enemy combatant."
"We will prosecute this terrorist through our civilian system of justice," Carney said, after some Republicans had said Tsarnaev should have the same status as the "war on terror" detainees held in Guantanamo Bay.
"The system has repeatedly proven that it can successfully handle the threat we continue to face," Carney said, adding that US law forbids trying citizens in military courts.
Tsarnaev was captured after a massive manhunt that virtually shut down Boston and its suburbs on Friday. His brother and alleged accomplice Tamerlan, 26, had been killed in a chaotic overnight shootout with police.
It was still unclear if the younger Tsarnaev's severe throat injury came at the hands of police or was self-inflicted in a suicide attempt. He is reportedly unable to speak but is communicating with authorities in writing.
As counterterrorism agents trained in interrogating "high-value" detainees waited at Beth Israel Deaconess Medical Center to learn more from the teen, Bostonians attempted to put the traumatic week behind them.
The city honored the victims of the blasts with a moment of silence at 2:50 pm (1850 GMT) that was also observed in other cities -- in Washington, by President Barack Obama and lawmakers, and in New York, at the stock exchange.
Hundreds gathered outside the security cordon set up near the blast sites at the marathon finish line on Boylston Street to honor the dead and wounded. Some prayed, others left flowers. Church bells rang out across the city.
"I am here for a friend seriously injured and for all the victims," teacher John Abbott, who was unable to finish last week's race, told AFP.
Businesses and restaurants are still shuttered inside the six-block area sealed off for the investigation, and residents living within the security cordon were forced to find temporary housing.
"I feel that I've been living in a movie for a week," sushi restaurant owner Chanjuda Bun told AFP. "We were closed three days last week and lost a lot of money -- we need to catch up now."
An affidavit by an FBI agent released Monday describes Tsarnaev as chillingly calm after the first of two bomb blasts -- part of why investigators believe he is to blame.
They are still hoping to get answers from Tsarnaev about the brothers' possible motive, and learn whether other attacks were in the works.
Boston Police Commissioner Ed Davis said Sunday that the brothers, who had been living legally in the United States for more than a decade, had more homemade explosive devices and appeared to have been planning more attacks.
He said federal authorities were trying to track down how and where the two suspects obtained firearms and explosive devices. An M-4 assault rifle was recovered in the boat where Dzhokhar was captured, the New York Times reported.
The brothers also apparently used two handguns and a BB gun in the shootout with police in the Boston suburb of Watertown. They are also believed to have shot dead a campus police officer at the Massachusetts Institute of Technology.
The motive for the attacks remains unclear, and investigators are now probing a six-month trip made by Tamerlan in 2012 to Russia's troubled regions of Dagestan and Chechnya, and whether he was radicalized or trained there.
Tamerlan had begun posting militant videos on social media sites in recent years. Both Russian regions are home to Islamist and separatist groups, but rebels in Dagestan have denied any link to the Boston bombings.
The elder Tsarnaev was questioned by the FBI, at Moscow's request, in 2011, but apparently was not seen as a threat.
The Tsarnaev family came to the United States from the former Soviet state of Kyrgyzstan around 2002. Dzhokhar became a US citizen in 2012, while Tamerlan's application was reportedly held up due to the FBI questioning.