U.S. authorities have charged the Boston Marathon bombing suspect with using a weapon of mass destruction, meaning if he is convicted he could face the death penalty for last week's explosions that killed three people and injured more than 170 others.
The 19-year-old suspect, Dzhokhar Tsarnaev, was charged in his hospital room Monday, while authorities continued to look for a motive behind the twin blasts near the finish line of the race. He also was charged with malicious destruction of property.
Attorney General Eric Holder said the investigation is continuing. He said, "We will hold those who are responsible for these heinous acts accountable to the fullest extent of the law."
Tsarnaev remained hospitalized under guard, lapsing in and out of consciousness and unable to speak to investigators. He is suffering a gunshot wound to his throat, although it is unclear whether it came from a shootout with police or was self-inflicted. However, Tsarnaev is reported to be answering some questions in writing.
After Boston's virtual lockdown on Friday during the manhunt for Tsarnaev, the city returned to some sense of normalcy Monday. Commuters filled major highways leading into city, children walked to schools and businesses opened their doors on the first day of the work week.
Deadly bombings in the United States
April 15, 2013: Twin blasts at the Boston Marathon kill at least 3, injure more than 140
September 11, 2001: Hijacked jets crash into World Trade Center, Pentagon and a Pennsylvania field killing nearly 3,000
July 27, 1996: Atlanta Summer Olympics bombing kills 2, injures more than 100
April 19, 1995: Car bomb at Oklahoma City federal building kills 168, injures more than 500
February 26, 1993: Van explosion in World Trade Center garage kills 6, injures more than 1,000
December 29, 1975: Bomb at New York's LaGuardia Airport kills 11, injures 75
September 16, 1920: Bombing in New York's Wall Street area kills 40, injures hundreds
Boston, a large, major city in the northeastern U.S., was set to hold a moment of silence Monday at 2:50 p.m. local time to mark the passing of a week since the deadly explosions. Bells are scheduled to ring throughout Boston and in other parts of Massachusetts to mark the solemn occasion.
A private funeral was set for one of the bomb victims, a restaurant catering manager, as well as a memorial service for a university graduate student killed in the blasts.
On Sunday, Boston's top police official said investigators believe the two brothers suspected in the bombings, Dzhokhar Tsarnaev and his older brother Tamerlan, were planning other attacks.
An investigator walks across Boylston Street near the site of the bombings in Boston, April 21, 2013.
Boston Police Commissioner Ed Davis said on CBS' "Face the Nation" program that authorities found a cache of homemade explosives after the gun battle between police and the Tsarnaev brothers. Davis said the scene was littered with unexploded bombs, and police found one improvised explosive device in the vehicle the brothers are accused of stealing.
The elder brother, 26-year-old Tamerlan, died in the shootout Thursday, while the younger Dzhokhar escaped, only to be captured alive hiding in a boat parked in the back yard of a suburban Boston resident.
The two suspects are ethnic Chechen immigrants who came to the United States as boys. Authorities have given no indication as to what motivated the brothers. So far, authorities say they do not believe the brothers were affiliated with a larger terrorist network and that they had acted alone.
Travel records show that last year Tamerlan Tsarnaev spent six months in Dagestan and Chechnya, predominantly Muslim republics in the north Caucasus region of Russia with active militant separatist movements.
U.S. investigators interviewed him in early 2011 at the request of "a foreign government," acknowledged by U.S. officials to be Russia.
A U.S. FBI statement late Friday indicated the request said Tamerlan had become a follower of radical Islam "and that he had changed drastically since 2010 as he prepared to leave the United States for travel to Russia's region to join unspecified underground groups."