EL CAJON — A 10-year-old boy reportedly being treated for anger issues is suspected of stabbing a 12-year-old friend to death at the younger boy’s East County home Monday, stunning their tight-knit neighborhood.

The assault occurred in the driveway of the home in unincorporated El Cajon. The 10-year-old is believed to have used a kitchen knife to stab his friend in the chest and then stayed while paramedics took his friend away.

The victim, who lived in the neighboring Knolls Mobile Estates on Royal Road, died upon arrival at a hospital.

Homicides by children that young are rare.

In 2010, U.S. law enforcement agencies reported 11 murder suspects under the age of 13 — the same number reported in 2009 and 2008, according to FBI data.

“On our end, we conduct this investigation as we would any homicide investigation,” said sheriff’s homicide Lt. Larry Nesbit. “What ultimately happens with the case will be up to the juvenile justice system.”

Authorities did not release the name of the suspect because he is a juvenile.

Neighbors said he attends W.D. Hall Elementary School. The name of the victim also was not released, pending notification of family. Neighbors said he attended St. Kieran’s Catholic School.

The suspect’s mother was at the one-story home in the Winter Gardens neighborhood when the attack occurred about 1:30 p.m., Nesbit said.

He would not provide details about the altercation, nor give a possible motive.

The 10-year-old boy was taken into custody by sheriff’s deputies, although it remained unknown if he would be booked into Juvenile Hall due to his young age.

Neighbors described the boys as part of a group of about eight friends who often played at various homes on the street. Many said the 10-year-old suspect’s emotional issues were well-known in the neighborhood.

Neighbor Derek Gorton, 18, who lives in the mobile home park, said that something as small as tapping the boy on the shoulder the wrong way or losing at a video game could set him off.

“Even though he threw temper tantrums, we never thought he’d do anything like this,” said Gorton, a senior at Santana High School in Santee.

Gorton’s father, Brian Richeson, a retiree who often had the boys at his home, said the suspect would usually express his anger verbally, not through violent acts such as throwing items or hitting people.

He said the boy’s mother was proactive in dealing with the problems.

“She was the best mom I’ve ever met,” Richeson said. “She knew how to take care of him if he was yelling and screaming.”

Richeson said all of the children in the neighborhood were like siblings — they would fight one hour and then be back to being best friends the next.

Point Loma family psychologist Rochelle Perper said sometimes it’s not easy to predict violent outbursts.

“Sometimes there is a buildup of pressure we might not really see. A child might be processing it internally, or it will come out in ways not widely recognized,” Perper said. “There have been cases reported when stress reaches a critical point, the response is drastically exaggerated for the situation.”

Perper said it would be a “big stretch” to charge a 10-year-old as an adult, especially if mental issues are diagnosed.

“More likely there will be a lot more psychological care. The focus should be on rehabilitating someone that young,” she said.

Eight-year-old Christian Romero, who fatally shot his father and a family friend in the small Arizona town of St. Johns in 2009, is one of the youngest killers in recent history. The boy pleaded guilty to voluntary manslaughter and was sentenced to residential treatment.

In San Diego County, the youngest killer in recent years was a 10-year-old boy who pleaded guilty in Juvenile Court to involuntary manslaughter in 1991. He fired the bullet that pierced a trailer wall in Barrio Logan and killed a woman as she tucked her son into bed. He was placed in a 24-hour school for a period of up to nine years.