In what police described as a horrific tragedy, a 9-year-old boy was shot and killed in his family’s Mattapan apartment by his 14-year-old brother Friday morning, anguishing neighbors and prompting a plea from the city’s mayor for residents to surrender unwanted guns.
Just before noon on a school day, the older brother was playing with a gun when it fired, striking the younger boy in the chest, police said. The boy was rushed to Boston Medical Center, where he was pronounced dead.
The older boy left his Morton Street home, but was apprehended nearby still carrying the weapon police said was used to shoot his brother.
“He was very remorseful for what he did,” William Evans, the city’s police commissioner, said at the scene, adding that the boy appeared to have panicked. “I think he realized the gravity of what he had done.”
The victim is the youngest person killed in the city since 2010, when 2-year-old Amanihotep Smith was shot in his mother’s arms after a home invasion in Mattapan.
The mother of the boys was not home at the time of the shooting, Evans said. It was not clear why they were not at school. The younger boy, found by police lying on his back in the hallway of his home, was in the fourth grade at James W. Hennigan Elementary School in Jamaica Plain.
The school notified parents of the shooting in a voice mail and counselors were on hand for students.
Authorities charged the 14-year-old with unlawful gun possession and involuntary manslaughter, saying that he was handling the gun recklessly when it fired.
There was no evidence that anyone else in the home knew he had the gun, they said.
Authorities were quick to call the shooting an apparent accident, but homicide detectives continued their investigation Friday.
Last June, police responded to the same address for a domestic violence report in which the 14-year-old allegedly slapped his younger brother in the face and threw him to the ground. His older teenage sister told police that he then pushed his mother to the ground and threatened to kill her.
In a police report on that visit, the sister stated the brother had “been very aggressive toward the family lately and that this was not the first time the police were called to their residence.”
The mother also told police that it was “not the first time” she had problems with her 14-year-old, according to the report. The older brother was charged with assault in the June incident.
Neighbors and police also said that officers had been previously called to the three-decker on Morton Street because of loud parties and, in one case, a shooting.
A law enforcement official briefed on Friday’s shooting said that “everything we are looking at it indicates it was accidental.”
“The brother was playing with the gun, pulled the magazine, and there was one bullet in the chamber,” said the official, who spoke on the condition his name not be published.
Authorities were attempting to determine how the brother acquired the gun and whether he knew a bullet was in the chamber.
The name of the older boy was withheld by authorities because of his age. Investigators also did not release the name of the victim.
Evans said he arrived at the home just as emergency responders were rushing the younger child to an ambulance.
“To see a young boy, curly hair, with so much life to live,’’ Evans said, his voice wavering with emotion. “Having three children myself, it just breaks your heart.”
Evans said the boys’ mother was “extremely distraught.”
In a prepared statement Friday, the Department of Children and Families, the state’s child welfare agency, declined to say whether it had any involvement with the family.
At the scene, Mayor Martin J. Walsh called the death a tragedy and urged residents to turn in guns to police.
“A 14-year-old should not have access to a gun,” he said. “There are far too many guns in our streets.”
“I’m calling for the community to step up to the plate and report these guns. Parents, siblings — we need to get these guns off the street,” he added.
Daniel Conley, the Suffolk district attorney, said investigators would work to determine how the boy acquired the weapon.
“In the meantime, I want to make something crystal clear: If you know about an illegal firearm in this city, help us prevent another tragedy like this one,” he said.
The 14-year-old was scheduled to be arraigned Monday in a closed hearing in juvenile court.
US Attorney Carmen M. Ortiz also said members of the community need to do more to track down guns in their homes and turn them over to police.
“You have to get the message out into the community that we share a sense of responsibility,” she said.
“The solution is not just law enforcement. The community has to be involved, do what they can, and cooperate with police.”
State Representative Gloria Fox, who represents Roxbury, visited the home with a grief counselor, saying the tragedy underscores the need for stricter gun control measures.
“I don’t know where that gun came from, but it should not have been in that young boy’s hands,’’ she said. “We’ve got to stop the trafficking of guns into our neighborhoods.”
In a neighborhood long plagued by gun violence, the death of a boy so young touched off a wave of grief and anger.
“Why would someone so young have a gun?” said Debra Brown, 54. “Why weren’t they in school? Where were the parents? It shouldn’t have to be this way.”
On Morton Street, residents decried the easy availability of guns, even for young teenagers, and the fear that pushes them to buy weapons.
“The sad thing is it’s so easy to get a gun in Boston,” said Nelson Martinez, 43. “He probably didn’t have to look very hard.’’
Cosandra Harrigan, 44, said there have been numerous shootings in the neighborhood in recent years, including one last summer in front of the same Morton Street home.
“Last summer they had a wild party, and somebody got shot in front of the same house, too, and died,’’ said Harrigan. “I’ve been here 17 years, and I’ve witnessed a lot of shootings.’’
“That’s the second shooting that has happened here,’’ said Ebony Rhodes, 20, of Dorchester. That’s crazy. It’s shocking.”
The shooting recalled for some the 2007 death of Liquarry Jefferson Jr., a first-grader who was shot to death by his 7-year-old cousin while they were playing with a gun left inside their apartment by a relative.
Jefferson was 8 when he was shot on June 24 of that year. He and his cousin had found a loaded 9mm handgun in the dresser drawer of Jayquan McConnico, an older cousin.
Despite the cold weather Friday, neighbors gathered near the home where the shooting occurred, saying they were struggling to come to grips with what had happened.
Celia Gabadon, 72, said that police are doing what they can and that change has to come from the community.
“Police are doing a good job,” she said. “We are to blame.”
Correction: Because of incorrect information provided to the Globe, an earlier version of this story misstated the age of the victim. He was 9.