UPDATED 7:59 p.m.: Prosecutors charged Dzhokhar Tsarnaev for the Boston Marathon bombings in an impromptu hearing on Monday in his hospital room, accusing him of crimes that could carry the death penalty if he is convicted.
Video taken by security cameras showed the 19-year-old ethnic Chechen placing a backpack near the finish line of the race one week ago, the criminal complaint said, alleging he acted in concert with his older brother, who was killed during a shootout with police early Friday.
Dzhokhar Tsarnaev was captured later that day after a massive manhunt and taken to the hospital with gunshot wounds.
The criminal complaint did not mention a motive for the bombings, leaving that as one of the mysteries of the investigation.
But a sworn FBI statement in support of the criminal complaint did reveal new details, such as the recollection of a man whose car was allegedly hijacked by the brothers while they tried to escape on Thursday night.
"Did you hear about the Boston explosion?" one of the brothers is said to have told the carjack victim. "I did that."
The brothers carried two backpacks containing pressure cooker bombs that ripped through the crowd near the finish line of the world renowned race, killing three people and wounding more than 200, the complaint said.
Ten people lost limbs from the bombs packed with nails and ball bearings. By Monday, Boston-area hospitals were still treating at least 48 people, with at least two listed in critical condition.
The charges were delivered on the same day Canadian police said they had thwarted an "al Qaeda-supported" plot to derail a passenger train. U.S. officials said the attack would have targeted a rail line between New York and Toronto, but Canadian police did not confirm that.
The 10-page complaint in the Boston case drew from investigators' review of a mass of video and still images captured by security cameras, the media and the public at the race before and after the bombing.
Thirty seconds before the first explosion, Dzhokhar Tsarnaev started fidgeting with his cellphone, the complaint said. After the blast, virtually everyone around him turned to look in that direction "in apparent bewilderment and alarm," while Dzhokhar Tsarnaev appeared calm, the complaint said.
He then left his backpack on the ground and walked away, the complaint said. About 10 seconds later the second explosion ripped through the crowd.
The charges were issued shortly before the city paused at 2:50 p.m. (1850 GMT) to mark the moment a week ago when the bombs exploded. A funeral was held for Krystle Campbell, a 29-year-old restaurant manager who was killed in the bombings, and a memorial service was planned for another victim, Chinese graduate student Lingzi Lu, 23.
An 8-year-old boy, Martin Richard, was also killed.
Dzhokhar Tsarnaev was wounded during at least one of two gun battles with police on Friday, suffering gunshot wounds to his head, neck, legs and hand, the complaint said.
He was mostly unable to speak due to a throat wound, managing to say "no" once in response to a question, according to a court transcript posted on the New York Times website. Mostly, he nodded in response to questions.
Magistrate Judge Marianne Bowler found he was lucid and aware of the nature of the proceedings, the transcript said.
His capture capped a tense 26 hours after the FBI released the first pictures of the two bombing suspects, still unidentified, on Thursday.
Five hours after their faces were pictured on TV screens and websites around the world, the brothers shot and killed a university policeman, carjacked a Mercedes and sought to evade police by hurling more bombs at them during a shootout on the streets of a Boston suburb, police said.
Older brother Tamerlan Tsarnaev, 26, was shot during a close-range exchange of gunfire with police and run over by his younger brother during his escape, police said. Dzhokhar Tsarnaev later abandoned the car and fled on foot, evading police for nearly 20 more hours until he was found hiding and bleeding in a boat.
Those extraordinary days captivated the United States and reminded people of the September 11, 2001, attacks.
"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," U.S. Attorney General Eric Holder said in a statement.
In choosing the civilian justice system, U.S. authorities opted against treating Tsarnaev, a naturalized U.S. citizen, as an enemy combatant.
Tamerlan Tsarnaev, a legal U.S. resident, visited relatives in the volatile region of Chechnya for two days during his six-month trip out of the United States last year, his mother, Zubeidat Tsarnaeva and aunt, Patimat Suleimanova, told Reuters in Dagestan on Monday.
U.S. investigators were trying to piece together if he may have become radicalized and determine whether he became involved with or was influenced by Chechen separatists or Islamist extremists there.
That trip, combined with Russian interest in Tamerlan Tsarnaev communicated to U.S. authorities and an FBI interview of him in 2011, have raised questions whether danger signals were missed.
The Tsarnaev brothers emigrated to the United States a decade ago from Dagestan, a predominantly Muslim region in Russia's Caucasus. Their parents, who moved back to southern Russia some time ago, have said their sons were framed.
A grand jury was likely to charge Tsarnaev with more crimes, said former federal prosecutor and University of Notre Dame law professor Jimmy Gurulé, calling the prosecutors' complaint preliminary.