Story highlights 8-year-old bombing victim Martin Richard reportedly attended marathon with his family

Richard's father was a spectator, a family spokesman tells CNN

His mother and sister were seriously injured and hospitalized, WHDH reports

Candlelight vigil planned Tuesday; boy's father thanks community

Almost a year ago, 8-year-old Martin Richard wrote four simple words on a sign at school.

"No more hurting people," it said.

For the camera, he held up the bright blue sign decorated with hearts framing the word "Peace."

It's a photograph that many find difficult to look at Tuesday as they struggle to comprehend the violence that took Martin's life. On Monday, the boy and his family were watching the Boston Marathon near the finish line when two bombs exploded just off Copley Square in the heart of the city.

The grade-schooler was killed, authorities said.

Photos: Deadly attack at Boston Marathon Photos: Deadly attack at Boston Marathon An injured man is loaded into an ambulance after two bombs went off near the finish line of the Boston Marathon on April 15, 2013. Three people were killed and at least 264 were injured. Hide Caption 1 of 55 Photos: Deadly attack at Boston Marathon A man comforts a victim on the sidewalk at the scene of the first explosion. Hide Caption 2 of 55 Photos: Deadly attack at Boston Marathon The second explosion goes off near the finish line. Hide Caption 3 of 55 Photos: Deadly attack at Boston Marathon The first explosion knocked down 78-year-old runner Bill Iffrig at the finish line. He got up a few minutes later and finished the race. Hide Caption 4 of 55 Photos: Deadly attack at Boston Marathon A runner embraces another woman on the marathon route near Kenmore Square. Hide Caption 5 of 55 Photos: Deadly attack at Boston Marathon Former New England Patriots offensive lineman Joe Andruzzi carries a woman from the scene. Hide Caption 6 of 55 Photos: Deadly attack at Boston Marathon A victim of the first explosion is helped on the sidewalk of Boylston Street. Hide Caption 7 of 55 Photos: Deadly attack at Boston Marathon An injured person is taken away from the scene in a wheelchair. Hide Caption 8 of 55 Photos: Deadly attack at Boston Marathon A woman kneels and prays at near the finish line. Hide Caption 9 of 55 Photos: Deadly attack at Boston Marathon People run down Exeter Street after the blasts. Hide Caption 10 of 55 Photos: Deadly attack at Boston Marathon The explosions occurred around 2:45 p.m., about an hour after the first of the race's nearly 27,000 runners had crossed the finish line. Hide Caption 11 of 55 Photos: Deadly attack at Boston Marathon Victims lie on the ground at the scene of the first explosion. Hide Caption 12 of 55 Photos: Deadly attack at Boston Marathon A couple runs from the scene pushing a stroller. Hide Caption 13 of 55 Photos: Deadly attack at Boston Marathon A runner reacts near Kenmore Square after the explosions. Hide Caption 14 of 55 Photos: Deadly attack at Boston Marathon A man's blood-stained feet hang outside an ambulance. Hide Caption 15 of 55 Photos: Deadly attack at Boston Marathon A bystander who was injured in the first explosion is wheeled across the finish line while receiving medical attention from rescue workers. Hide Caption 16 of 55 Photos: Deadly attack at Boston Marathon Carlos Arredondo was at the race handing out American flags to spectators. After the blasts, he helped emergency responders and is credited with helping a man survive serious leg wounds. Hide Caption 17 of 55 Photos: Deadly attack at Boston Marathon The second explosion goes off near the finish line. Hide Caption 18 of 55 Photos: Deadly attack at Boston Marathon Police look at blown-out windows. The bombs shook buildings, witnesses said, sending people to seek shelter under tables. Hide Caption 19 of 55 Photos: Deadly attack at Boston Marathon Unclaimed runners' bags fill an area near the marathon finish. Hide Caption 20 of 55 Photos: Deadly attack at Boston Marathon Women desperate to hear from loved ones are unable to get close to the site of the attack. Hide Caption 21 of 55 Photos: Deadly attack at Boston Marathon Police and runners stand near Kenmore Square after the attack. Hide Caption 22 of 55 Photos: Deadly attack at Boston Marathon Runners gather near Kenmore Square after the explosions. Hide Caption 23 of 55 Photos: Deadly attack at Boston Marathon An EMT worker is transferred to an ambulance outside a medical tent in Copley Square. Hide Caption 24 of 55 Photos: Deadly attack at Boston Marathon A SWAT team arrives on the scene. Hide Caption 25 of 55 Photos: Deadly attack at Boston Marathon A runner sits near Kenmore Square after the attack. Hide Caption 26 of 55 Photos: Deadly attack at Boston Marathon Runners who had not yet finished the race are stopped after the explosions. Hide Caption 27 of 55 Photos: Deadly attack at Boston Marathon Victims are helped at the scene of the first explosion. Hide Caption 28 of 55 Photos: Deadly attack at Boston Marathon A man in tears is helped at the scene on Boylston Street. Hide Caption 29 of 55 Photos: Deadly attack at Boston Marathon Passersby put pressure on a victim's leg to try to stop the bleeding. Hide Caption 30 of 55 Photos: Deadly attack at Boston Marathon Massachusetts State Police guard an area near Kenmore Square. Hide Caption 31 of 55 Photos: Deadly attack at Boston Marathon Bystanders embrace near the finish line. Hide Caption 32 of 55 Photos: Deadly attack at Boston Marathon Police officers gather on Newbury Street. Hide Caption 33 of 55 Photos: Deadly attack at Boston Marathon Women and children are escorted away from the scene. Hide Caption 34 of 55 Photos: Deadly attack at Boston Marathon Bomb squad officials check a possible suspicious device near the scene of the blasts. Hide Caption 35 of 55 Photos: Deadly attack at Boston Marathon A woman is comforted after the blasts. Hide Caption 36 of 55 Photos: Deadly attack at Boston Marathon Two injured women are taken away on stretchers. Hide Caption 37 of 55 Photos: Deadly attack at Boston Marathon An injured woman is loaded into an ambulance. Hide Caption 38 of 55 Photos: Deadly attack at Boston Marathon First responders load injured people into an ambulance. Hide Caption 39 of 55 Photos: Deadly attack at Boston Marathon An injured man is prepared to be moved from a stretcher to an ambulance. Hide Caption 40 of 55 Photos: Deadly attack at Boston Marathon An injured woman is placed on a stretcher. Hide Caption 41 of 55 Photos: Deadly attack at Boston Marathon A runner is comforted following the attack. Hide Caption 42 of 55 Photos: Deadly attack at Boston Marathon The Cambridge Police Department's bomb squad investigates unattended personal items left behind after the explosions. Hide Caption 43 of 55 Photos: Deadly attack at Boston Marathon Bystanders check their mobile devices for news of the explosions. Hide Caption 44 of 55 Photos: Deadly attack at Boston Marathon A member of the bomb squad investigates a suspicious item on the road near Kenmore Square. Hide Caption 45 of 55 Photos: Deadly attack at Boston Marathon A runner in a wheelchair is taken from a triage tent after the explosions went off. Hide Caption 46 of 55 Photos: Deadly attack at Boston Marathon People comfort each near the site of the blasts. Hide Caption 47 of 55 Photos: Deadly attack at Boston Marathon Racers and race officials stand by after the explosions. Hide Caption 48 of 55 Photos: Deadly attack at Boston Marathon Emergency personnel respond to the scene. Hide Caption 49 of 55 Photos: Deadly attack at Boston Marathon Police and emergency crews tend to victims. Hide Caption 50 of 55 Photos: Deadly attack at Boston Marathon An injured woman is carried away on a stretcher. Hide Caption 51 of 55 Photos: Deadly attack at Boston Marathon A man lies on the ground after the incident. Hide Caption 52 of 55 Photos: Deadly attack at Boston Marathon Officials watch as the first explosion goes off on Boylston Street. Hide Caption 53 of 55 Photos: Deadly attack at Boston Marathon Spectators leave the bleachers after the explosions. Hide Caption 54 of 55 Photos: Deadly attack at Boston Marathon Police inspect one of the blast sites. Hide Caption 55 of 55

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Denise Richard underwent surgery for an injury to her brain, and Martin's 6-year-old sister lost her leg, CNN affiliate WHDH reported. As of 1 p.m. ET Tuesday, both were still hospitalized, according to WHDH.

The boy's father, William Richard, is a community leader in the Ashmont section of Dorchester, according to the Globe.

"My dear son Martin has died from injuries sustained in the attack on Boston," Richard said in a statement Tuesday. "My wife and daughter are both recovering from serious injuries. We thank our family and friends, those we know and those we have never met, for their thoughts and prayers. I ask that you continue to pray for my family as we remember Martin. We also ask for your patience and for privacy as we work to simultaneously grieve and recover. Thank you."

After early reports conflicted about whether William Richard ran the marathon, a family spokesperson told CNN Tuesday afternoon that he was a spectator.

Tuesday morning, people arrived at the Richards' home in the working-class neighborhood dotted with large New England-style homes. On the stone steps of the Richards' blue-gray house, visitors gingerly laid down flowers. Someone had written "peace" at the end of the driveway, according to the Globe.

More than a 1,000 people, many holding candles and each other, attended a vigil in Dorchester for Martin and the other two victims Tuesday night.

Neighbor Jane Sherman told CNN that William Richard came home Monday night about 10:30. He seemed extremely upset and didn't appear to want to talk, she said.

On Tuesday at the Richard home, a 10-year-old girl who went to school with Martin came by with her mother.

"We came here to pay our respects," the mother told CNN. "My daughter was very sad. He was a very nice boy."

Martin attended the Neighborhood House Charter School, according to a school official.

The boy "was a bright, energetic young boy who had big dreams and high hopes for his future, the school said in a statement. "We are heartbroken by this loss."

"We are also praying for his mother Denise, our school librarian and sister Jane, another Neighborhood House Charter student, who were seriously injured yesterday," the statement said.

The family represent "the very best this city has to offer," it said.

Also killed in Monday's attack was Krystle Campbell, who graduated from Medford High School in Massachusetts in 2001. There were no immediate details about the third victim killed in the bombings. Of the more than 170 people who were treated at hospitals, at least 17 were in critical condition and 41 in serious condition, according to hospital officials.

Martin made his "peace" sign in May when his school organized a "Peace Walk." Holding their homemade signs, kids walked around the city making a big statement with a simple act. In bubble letters, one of his classmates wrote, "No more violence!"

In another photo of Martin -- this one apparently marking what was perhaps his first communion -- he is smiling, missing a few teeth, handsome and proud in his white suit. He holds a colorful communion banner. On it is a dove that symbolizes the Holy Spirit.

The Richard family was very active in the neighborhood.

"They are beloved by this community," City Councilor at Large Ayanna Pressley told the Globe. Pressley and other devastated residents gathered at Tavolo Restaurant in Dorchester to mourn.

The family contributes "in many ways," she said. "That's why you see this outpouring. It's surreal; it's tragic."

Sherman said that the Richard family is a "typical all-American family" and that Martin and his little brother always loved to play in their yard, no matter the weather.

Neighbor Dan Aguilar told The Boston Globe the same and said he was having a hard time wrapping his mind around the child's death.

"That little boy will never come home again,'' he told the paper. "It's still unreal. I have no words. I have no words.''

While so much grieving continues, more details are emerging about Monday's bombings.

No suspects have been identified in the case, which federal authorities are classifying as an act of terrorism. It was not immediately known whether the origin of the bombings was domestic or foreign.

The intelligence community is poring through all threat reporting for any clues, U.S. counterterrorism officials told CNN. That includes any claims made on jihadist websites.

Nothing is being dismissed this early on, the officials said.