Boston bombing suspect Dzhokhar Tsarnaev could face the death penalty after being charged for his alleged role in the attacks that left three people dead and 200 wounded.
The 19-year-old was said to be alert as he was arraigned in his hospital bed on charges of using and conspiring to use a weapon of mass destruction, and malicious destruction of property by means of deadly explosives, the US Department of Justice said.
The charges came as Boston marked the one-week anniversary of the twin marathon bombings with a moment of silence observed across the nation, including the White House to the New York Stock Exchange.
If Tsarnaev, a naturalized US citizen of Chechen descent, is convicted of the federal charges, he faces time behind bars -- or even 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 gunshot wounds to the head, neck, legs and hand before his capture 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 called for Tsarnaev to have the same status as the "war on terror" detainees held in Guantanamo Bay.
Tsarnaev was caught 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.
A clearer picture of Tsarnaev's role in the attacks emerged with the release of an affidavit from an FBI agent on Monday, which revealed the teenager had been caught on film planting the second backpack bomb.
Surveillance footage showed Tsarnaev calmly walking away from the scene after the first bomb was detonated, according to the affidavit.
Tsarnaev, who remains bedridden and hospitalized, spoke only one word aloud at his bedside hearing Monday, responding "no" when asked whether he could afford an attorney, according to a transcript of the hearing released Monday.
Otherwise, the record showed he nodded when asked whether he understood the process and the charges against him. The federal judge said she found him "alert, mentally competent, and lucid," according to the transcript.
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 Washington, by President Barack Obama and lawmakers, and in New York, at the city's 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.
FBI investigators are still hoping to get answers from Tsarnaev about the brothers' possible motive, and learn whether other attacks were in the works.
An unnamed US government source told CNN that "preliminary interviews with Tsarnaev indicate the two brothers fit the classification of self-radicalized jihadists," and that international groups were not involved.
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.
US Senator Lindsey Graham said the FBI and Russian intelligence may have missed warning signs and made basic errors like misspelling Tamerlan Tsarnaev's name, allowing him to travel to Russia undetected.
"I've been told by the FBI that the reason that his name did not pop up in the system was because it was misspelled," Graham said.
"We don't know if he misspelled it," or if it was the fault of the airline, identified by Graham as Russian flagship Aeroflot.
"We certainly missed it here."