(CNN) -- A college student embarks on a shooting spree, taking 32 lives. A teenager with an assault rifle opens fire on holiday shoppers in a department store in middle America. And, long before that, two youths turn the halls of their high school into a virtual abattoir, leaving some 13 dead before killing themselves.
Mourners attend a candlelight vigil for victims of the Omaha, Nebraska, mall shootings earlier this week.
Blame for the explosion of violence by teenagers and young adults in recent years has fallen on everything from the breakdown of families to video games, from lax security to violent music.
In reality, experts say, a variety of societal factors is behind youth violence. But, they maintain, it is not an unavoidable consequence of life in the 21st century: It can be reduced, if not prevented entirely, through programs aimed at increasing awareness and education, reducing the stigma sometimes associated with mental illness or depression, and providing youth with the skills and confidence needed to handle difficulties.
"We've learned a lot about what works," said Tom Simon, deputy associate director for science for the Centers for Disease Control's Division of Violence Prevention. "There's only so much we can do as a society to keep the places where we gather safe -- metal detectors, guards, cameras. The need, really, is to focus on primary prevention. We need to start early."
'At least I can be notorious'
Youth violence rocketed to the forefront of American consciousness in 1999, when Dylan Klebold and Eric Harris killed 12 of their fellow Columbine High School students and a teacher before turning their guns on themselves. The two live on in cyberspace, where they have gained a cultlike following among disgruntled youth -- and continue to inspire similar acts, experts say.
"A large number of people over the Internet ... idolize Klebold and Harris and consider them to be heroes," Montgomery County, Pennsylvania, District Attorney Bruce Castor said last month. Castor was speaking about a case in which a 14-year-old was arrested and accused of plotting to launch a Columbine-style attack at his former high school. See a timeline of notorious youth violence incidents »
That youth, Dillon Cossey, had contact via computer with Finnish teenager Pekka-Eric Auvinen, who on November 7 killed eight people at his high school outside Helsinki before committing suicide.
The two discussed their admiration for Klebold and Harris, as well as their interest in violent role-playing computer games, Castor said.
Louis Schlesinger, a forensic psychologist and professor of psychology at New York's John Jay College of Criminal Justice, pointed out that President John F. Kennedy and the Rev. Martin Luther King Jr. were both on the cover of Newsweek magazine once.
"Klebold and Harris were on the cover of Newsweek twice," he said. "What does that tell you?"
Teenagers and young adults, he said, got the message loud and clear. A suicide note left by Robert Hawkins, the 19-year-old gunman behind Wednesday's shootings at an Omaha, Nebraska, department store, says that he had been "a piece of sh-- all his life and that now he'd be famous," according to the woman who found it.
"He's thinking, 'OK -- I'm a nobody, I'm treated like dirt, at least I can be notorious,'" said Ralph Larkin, a research associate and adjunct professor at John Jay College and the author of the book "Comprehending Columbine." "That's what he thought when he went into the mall."
Hawkins killed eight people before turning his rifle on himself. See profiles of the victims »
Seung-Hui Cho, a Virginia Tech student who in April killed 32 students and faculty before shooting himself to death, was also fixated on Columbine, something noted in his middle and high school records.
Although there is an undeniable rise in youth violence in the past 30 years, Schlesinger points out that life in general is different than decades ago -- in schools and in families. For instance, there are more single-parent families, and in two-parent families, both parents are more likely to work outside the home. Those societal shifts have a ripple effect that may have unintended consequences, he said.
"It's in every area of society. It's so different."
In many cases, rampage shooters -- like Klebold and Harris -- are seeking revenge "for usually a long history of victimization, public humiliation, being bullied," Larkin said.
Or they may feel repeatedly rejected. According to Debora Maruca-Kovac, who let Hawkins live with her after he experienced problems at home, the teen was "kind of like a pound puppy nobody wanted."
He recently had broken up with his girlfriend, she said, and lost his job the day of the mall shootings. He previously had withdrawn from school, and was turned down when he attempted to join the Army. Watch how killer exhibited signs of trouble »
Hundreds of thousands of youth have similar experiences yet do not become violent, Schlesinger notes.
And "the majority of people with mental illness are not violent," said Terry Cline, an administrator with the federal Substance Abuse and Mental Health Services Administration (SAMHSA). "The majority of violence we see in our country is committed by people who are not mentally ill. There are millions of people in our country who are living successfully with mental illness."
However, in nearly every case of rampage shootings by youths, a clear pattern emerges -- after it's too late.
Warning signs of emotional disturbance are usually there, Cline said. But those who see it -- typically a youth's friends or fellow students -- are "not quite sure what to do with that."
In addition, he said, the stigma still attached to mental disturbances prevents people from asking for help or talking to someone about it.
"We want to make certain that people have a better understanding of those early warning signs and know what to look for," Cline said.
There are ways, both in and out of the classroom, to ensure that children don't grow into troubled, violent youths, experts maintain. And research has proved their effectiveness.
"There really is the potential if you start early and work with these kids," Simon said. "There really is promise for primary prevention."
Larkin advocates the need for a "peace education program" built into school curriculums that focuses on non-violent conflict resolution as well as issues such as bullying. "We have to build much stronger support networks for kids," he said.
Students who participate in such a universal school program -- aimed at impacting all the children in a school, not just those who are at risk for future violence -- have shown a 15 percent relative reduction in violent behavior, Simon said.
SAMHSA has launched a program called "What a Difference A Friend Makes," Cline said. It is aimed at educating young people on the signs of mental illness and emotional disturbance and encouraging them to provide support to friends who may be experiencing difficulty, rather than becoming awkward and uncomfortable and turning away.
"Their support may be critical to that person's recovery," he said.
The program, which targets 18- to 24-year-olds, involves public service announcements and other ads. In addition, information packets have been distributed to college students nationwide. SAMHSA is retooling it to target ethnic and racial minorities and will relaunch it in the near future, Cline said.
Focusing on the age group is important, he said. Half of all lifetime cases of mental illness are diagnosed by age 14, and three-quarters by the age of 24.
After-school programs can provide a youth with the opportunity to learn new skills and build a positive relationship with at least one adult, and mentoring programs can provide teens with a "supportive, nonjudgmental role model," according to the National Youth Violence Prevention Center, an organization that evolved from the White House-established Council on Youth Violence, the CDC and other agencies following the Columbine shootings.
A program called therapeutic foster care places troubled youths with a pattern of delinquent behavior into specially trained foster families for several months, Simon said. They are provided with a structured environment, where positive social behavior is rewarded and negative behavior is punished. Research has shown a 70 percent reduction in violent crime among youths participating in the program, he said.
Such programs, he acknowledged, are expensive to implement, which may be an obstacle.
Cline said SAMHSA attempts to maximize scarce funding by focusing on being proactive, rather than reactive.
"The key with the funding is that we be as strategic as possible," he said. "That's why we're focusing upstream with those issues. It's not targeting individuals who are already in the throes of mental illness.
"We are really emphasizing more of a public health approach. There are things we can do to decrease risk factors and increase resiliency ... so (youth are) less likely to have negative outcomes."
"Funding is always a problem," Simon said. But in the case of the therapeutic foster care program, for instance, a cost analysis has shown that for every dollar spent, $14 is saved that would be spent in the justice system -- meaning that making prevention a priority will pay off in the future.
"It really comes down to our willingness to go long-term," he said. E-mail to a friend
CNN's Joe Sterling and Tricia Escobedo contributed to this report.