A look at the basics of the Boston Marathon bombing investigation

A flag flies over the finish line as medical workers aid injured people following an explosion at the finish line of the 2013 Boston Marathon in Boston, Monday, April 15, 2013. (AP / Charles Krupa)

Two explosions near the finish line of the Boston Marathon on April 15 killed three people and wounded more than 200 others. Authorities launched a massive manhunt for two suspects seen on surveillance video before one died following a gun battle with authorities and police captured the second suspect alive. A look at the basics of the case:

THE MOTIVE

The suspects appear to have been motivated by a radical brand of Islam although they do not seem connected to any Muslim terrorist groups, say U.S. officials, who spoke on condition of anonymity because they were not authorized to discuss the investigation.

THE CHARGES

Federal prosecutors on Monday charged bombing suspect Dzhokhar Tsarnaev with using and conspiring to use a weapon of mass destruction to kill for what they say was his role in bombing the Boston Marathon.

Authorities charged him in his Boston hospital room, where he was being treated for serious wounds.

If found guilty, Tsarnaev could get the death penalty for what authorities say was a plot that he and his now-deceased older brother, Tamerlan Tsarnaev, carried out that killed three people and injured more than 200.

The criminal complaint cited surveillance-camera images of Tsarnaev dropping off a knapsack with one of the bombs and using a cellphone, perhaps to coordinate or detonate the blasts.

VICTIM TRIBUTES

Family, friends and dignitaries gathered Monday for a funeral service for bombing victim Krystle Campbell, celebrating her life as someone who was always there for others and loved to smile.

People who couldn't find seats inside Saint Joseph Church in Campbell's hometown of Medford, Mass., also lined the sidewalks outside during the service.

The 29-year-old restaurant manager was watching the race near the finish line with a friend when the bombs exploded last week.

Gov. Deval Patrick and Roman Catholic Cardinal Sean O'Malley were among public figures at the funeral, where Irish tenor Ronan Tynan sang "Ave Maria."

At a memorial service Monday evening for Lu Lingzi, a 23-year-old graduate student at Boston University, friends and family vowed not to forget the light in their lives that was extinguished too soon.

"You need us to be strong and brave," Jing Li said of her roommate, a native of northern China killed as she watched the marathon. "We will keep running to finish the race for you and we will try to realize your unfinished dream."

Patrick also was among the hundreds of people who attended the hour-long service.

MINUTE OF SILENCE

Bombing survivors, residents and state officials were among thousands gathered in silence across the Boston area Monday afternoon, one week after deadly explosions erupted near the Boston Marathon's finish line.

At 2:50 p.m. - exactly one week after the bombings - many bowed their heads and cried at the makeshift memorial on Boylston Street, three blocks from the site of the explosions. Bouquets of flowers, handwritten messages, and used running shoes were piled on the sidewalk.

Patrick bowed his head during the one-minute silent tribute while standing with other elected leaders on the front steps of the 215-year-old state capitol.

The governor then approached a microphone and said: "God Bless the people of Massachusetts. Boston Strong." No other words were spoken as church bells pealed throughout the city.

HOW THE SITUATION UNFOLDED

Surveillance tape late Thursday showed Dzhokhar Tsarnaev, Suspect No. 2, at a gas station. Authorities said the two suspects fatally shot a university police officer then carjacked a man and got involved in a chase with police that resulted in explosives being thrown from their car and an exchange of gunfire. Tamerlan Tsarnaev, Suspect No. 1, was wounded and died later at a hospital.

PUBLIC REACTION

After the death of one suspect and the capture of the other, people in Boston and its western suburbs thanked police, cheered, applauded and set off fireworks. Later, they gathered in silence near the site of the bombings to remember the victims. Some cried. Some wrapped themselves in American flags.

"Now I feel a little safer," Boston resident Beth Lloyd-Jones said.

THE SUSPECTS

Law enforcement officials and family members have identified the brothers as ethnic Chechens who had lived in Dagestan, in southern Russia. The brothers had been in the United States for about a decade and lived near Boston, an uncle said. Dzhokhar Tsarnaev, whose father has called him a "true angel," is a 19-year-old student at the University of Massachusetts at Dartmouth. Tamerlan Tsarnaev was a 26-year-old boxer. Their uncle Ruslan Tsarni called them "losers."

THE MARATHON EXPLOSIONS

Two bombs exploded about 10 seconds and 100 yards apart in Boston's Copley Square, near the finish line of the marathon. An 8-year-old boy, a 29-year-old woman and a 23-year-old graduate student from China were killed, and more than 200 people were wounded. The explosions occurred about four hours into the race and two hours after the winners had crossed the finish line, but thousands of runners were still on the course.

THE BOMBS

Authorities have said they believe the bombs used were fashioned out of ordinary kitchen pressure cookers packed with explosives, nails, ball bearings and metal shards. They say the bombs were hidden in backpacks and left on the ground.