The headlines this week have been unavoidable:

•In Massachusetts, 14-year-old Philip Chism sits in jail, charged with murdering Danvers High School teacher Colleen Ritzer and awaiting a grand jury decision about whether he should be tried as an adult.

•In Nevada, a 12-year-old boy is dead by a self-inflicted gunshot wound after killing a teacher and wounding fellow students at Sparks Middle School.

•In California, a boy who was 10 when he shot and killed his abusive neo-Nazi father awaits sentencing as a juvenile.

Each case is different, but collectively they may prompt people to wonder if more young Americans are turning into murderers. What can explain such killings? Can they be prevented? How should young killers be punished or redeemed?

The first question is easiest to answer – with data. Though it’s not much comfort to the victims of any particular crime, the number of juvenile homicide offenders in the US recently hit its lowest level in 30 years.

In 2011, there were 808 12- to 17-year-olds known to have committed homicides, down from 1,437 in 1980 and a peak of 2,800 in 1994, according to the FBI’s Supplementary Homicide Reports. Homicide by those younger than 12 is rare, with five offenders in 2011 and ranging between 0 and 30 offenders a year over the past 30 years.

“Nearly 20 years ago, we had half a dozen multiple-victim school shootings by students in America … and the same questions were being asked then: What’s the matter with kids today?” says James Alan Fox, a criminology professor at Northeastern University in Boston.

“Nothing’s different about kids,” he says, though 50 years ago, bullied kids might have been more likely to take their anger out through vandalism rather than pick up a gun. Kids today may more often fantasize about shooting up their schools because of “a change in the cultural scripts,” he says, but most of them don’t actually do it, and killings by kids are not at epidemic proportions.

Schools and students would be well-served today if they “upped the level of respect” through improving the overall climate for kids, but whether or not that will prevent school shootings isn’t known, Professor Fox adds.

People often struggle to understand the motive behind violent crimes, especially by children. Phil Chalmers was so interested in this question that he spent 25 years interviewing more than 200 young murderers and writing the book, “Inside the Mind of a Teen Killer.”

On the basis of those interviews, he speaks with groups all over the United States about 10 causes he identified. Usually three or more of these factors are present in a teen killer’s background, he says. The most common: an unstable home life or being bullied at school, obsession with violent entertainment, being suicidal, or involvement with drugs and alcohol. Among other common factors were gang or cult involvement, and mental illness.

Many teens experience several of those factors and few become killers. Mr. Chalmers teaches audiences to look for warning signs that someone may be headed toward violence. And if they’ve already seen such signs, he says, they have to be especially watchful for what might trigger someone to act on thoughts of violence. “The biggest trigger for a male teen killer is that his girlfriend dumps him,” he says. For girls, the most common trigger is being told by her parents that she can’t date a particular person.

Sometimes, teens kill while committing another crime, such as sexual assault. Sometimes they are seeking a thrill, Chalmers says.

The obsession with celebrity in society may share some blame, as well. A lot of young killers are “invisible at school, nobodies, and they know they are going to be famous if they kill,” says Chalmers.

Although most of the teen killers he interviewed will never get out of prison, Chalmers says, “the majority are remorseful.”

Some homicides by youths can be traced back to mental illness, but not most, Fox says.

Because adolescents tend to be more impulsive, their “reasons for killing are often trivial – a leather jacket, or someone looking at you the wrong way,” Fox says.

Brain research has contributed in recent years to the understanding that juveniles should be seen as “redeemable, because they are still developing,” says Naoka Carey, executive director of the Massachusetts group Citizens for Juvenile Justice. “They don’t have a lot of life experience to put their current situation in context…. They feel things very intensely. They have a breakup and it’s the end of their life because they’ve never gone through that before…. It doesn’t change the fact that they may have done something really terrible, but it changes the context of how we understand what happened.”

Acknowledging the science on adolescent development, the US Supreme Court ruled last year that mandatory life sentences without parole were unconstitutional for anyone under 18 at the time of the crime. Several years earlier, the court also outlawed the death penalty for offenders under 18.

In California, the boy who killed his father when he was 10 told police he was afraid he would have to choose between living with his father and his stepmother, who were headed for a divorce. He had a history of violence from a young age and was indoctrinated in the beliefs of white supremacy.

Living in a county juvenile hall, he has attended classes, has received regular therapy, and has made progress in controlling the violent outbursts that got him kicked out of various schools.

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A hearing is under way to determine whether he’ll continue to serve in a juvenile justice facility or be sent to a residential treatment center that defense attorneys say is better equipped to handle his emotional disabilities.

Material from Associated Press was used in this report.