Multiple bombs. An arsenal of guns. Months of detailed planning for killing his family and then unleashing explosives and bullets on his classmates at Waseca's junior and senior high school.

It was all meant to happen on April 20, the 15th anniversary of the rampage at Columbine High School, John David LaDue told police.

By chance, LaDue was arrested last week as he was making final preparations for the attack that he was forced to postpone in April when the 20th fell on Easter Sunday. But the shocking details of the arsenal that the 17-year-old high school junior had amassed — undetected and unsuspected — masked another disturbing fact: His fascination with Columbine was hardly unique.

Instead, the portrait of LaDue spelled out in criminal charges is that of just the latest angry, disturbed teen who fell prey to the "Columbine effect," deciding to vent his frustrations and alienation in a murderous replay of the nation's most infamous school massacre.

Twelve students and one teacher died that day in April 1999, along with the two teenage gunmen, who killed themselves. A decade and a half later, the images still resonate: the grieving parents, the scrambling police officers, the videos of the shooters taking target practice. For adolescents who may also be battling the first signs of mental illness, Columbine strikes a chord, according to a number of experts on school violence and student psychology.

"Shooters get their inspiration from different places, depending on their own grievances and their own background," said Bruce Shapiro, executive director of the Dart Center for Journalism and Trauma at Columbia University. "But there's no doubt that many of these shooters learn from past events."

Steve Brock, president-elect of National Association of School Psychologists and a member of a national emergency response team who has visited the sites of school violence, including the 2005 shootings in Red Lake, Minn., said LaDue's plans for Waseca look a lot like Columbine because he had a similar motivation: He wanted the same, shocked attention.

"Young people see these acts and the incredible amount of attention given to it and believe, somehow, they'll derive some benefit," said Brock, a professor and school psychology program director at California State University, Sacramento.

Dave Cullen, the author of the book "Columbine," said disturbed kids see the Littleton, Colo., massacre as "kind of like the template" for outsider students to exact revenge on the chief society they've known in their young lives, their schools.

LaDue in fact, "idolized" Columbine shooter Eric Harris and made several references to Harris and fellow shooter Dylan Klebold in a 180-page journal that spelled out details of his plan, according to the criminal complaint. LaDue even "critiqued what Harris and Klebold did right and wrong" during the shooting, law officers revealed.

"You've got teen boys. They are lashing out about all sorts of things. They don't know how to get themselves heard," Cullen said. "Until we figure it out and solve it and put an end to it, it's going to keep happening."

Case after case

Kenneth Trump, a national expert on school safety, said the Columbine anniversary can be a "trigger" each year, coming as it does near the end of another school year that can bring fresh slights or problems for kids on the edge.

In a May 2006 newspaper article in which he talked about Columbine-style conspiracies, Trump said that authorities across the country investigated 12 cases of students plotting a school shooting or making threats against schools in March and April of that year alone.

A year later, police in Connecticut broke up a plan by a 16-year-old to shoot up his high school. According to the Los Angeles Times, the boy had stockpiled guns in his bedroom closet and had a hit list of more than 20 classmates, along with photos of Harris and Klebold.

And in April 2008, a student in South Carolina was arrested for plotting to bomb his high school. In a search of the student's room, police found a journal in which the 18-year-old scribbled complimentary notes about the Columbine shooters.

Trump, in an interview Friday, said it's important to remember that schools can be subject to violence at other times of the year, too.

"The common theme here is undiagnosed or untreated mental health issues,'' he said. "When you peel the onion back in coming weeks, you are going to find there are many other issues — social, physical, mental health issues — that will come forth that were not known right after the event."

Some of those who know LaDue have described him as a "good" and a "quiet" boy who loved playing guitar, always said "thank you'' and was never in trouble at school.

Several friends and neighbors said they were "amazed" to learn the accusations against LaDue outlined in the criminal complaint.

Looking back, many in Waseca now wonder: What did they miss?

Several neighbors said they saw LaDue throwing knives and axes almost daily at tall pine trees in his front yard. One neighbor said that in hindsight, "it's kind of disturbing."

But until last week, apparently, nobody had a clue what the quiet teen was hiding.

"This is not something otherwise mentally health people do,'' Brock said. "All these perpetrators of these acts have mental health challenges."

Paying attention

Experts say a key to averting tragedy is making sure adults are attuned to the signs often given by troubled kids.

"If you're paying attention, you can see these kinds of acts coming," Brock said. "Someone doesn't wake up one morning and decide to blow up a school."

Everett Arnold, school superintendent in Red Lake, where 10 people, including the teen gunman, were killed and five others wounded in 2005, said the biggest lesson administrators learned from that tragedy was how important it is to develop relationships with each student.

"We just, as a staff and as a community, became much more attuned to mental health issues and tried to create a culture of inclusivity," Arnold said.

While school security was heightened and metal detectors and cameras were added, Arnold said that in the years since, administrators and teachers have regularly participated in training sessions that focus on student needs, especially the kids whose academic performance or behavior has changed.

Matt Hillmann, director of administrative services in the Northfield School District, said teachers there fill out a "connectivity" survey to ensure that each student has some sort of relationship with a teacher or staff member.

Earlier this school year, the district hosted an "active shooter" training event that involved extensive discussions about how to spot warning signs that a student might be troubled, Hillmann said.

In Bemidji, school officials are "listening now more for the signs than in the past," said Greg Liedl, transportation coordinator and liaison for emergency management for the school district.

Still, he added, sometimes those signs of trouble can be missed.

"It's the same thing that happens in teen suicides — you see that sign after it happened," Liedl said.

Preparation, and chance

Nancy Lageson, director of the state's School Safety Center and a retired police officer, said that in many ways, schools are "more prepared" for potential trouble than they were a generation ago.

"They have visitor procedures. They have controlled access. They have controlled doors," Lageson said. "When I was growing up, that was not the case."

Schools also are required by law to have a crisis management plan and threat assessment teams that assess a student's personality, family and school dynamics and the student's peer group to help determine risks.

The safety center trains school officials to respond to threats. Like other experts, Lageson said that establishing strong relationships with students is essential. A former in-school officer, Lageson said she recovered guns several times in school. Each time, she said, a student tipped her off.

Even with the greater scrutiny and awareness, Waseca came perilously close to disaster.

Bomb squad shocked

LaDue was caught just in time, and by a tip from a caller who thought a teen was acting suspiciously on a visit to a storage unit.

Bomb squad members called in to confiscate the explosives were "shocked by the amount of bomb making chemicals and components" he had in a storage unit, according to the criminal complaint. "Bomb squad members said they have never seen that much of some of those chemicals in one place."

Investigators found three bombs in LaDue's house and seven firearms in his bedroom, along with ammunition. Three more bombs were discovered at the storage unit, along with chemicals and materials to make them and 60 pounds of metal ball bearings. The storage unit also held a black trench coat, an item of clothing that the Columbine shooters were fond of wearing.

How near was Waseca to Columbine's fate?

Based on LaDue's statements to police and the completed bombs and weaponry found in his bedroom and storage unit, police concluded: "Officers believe that LaDue intended to carry out his plan to kill within the next week or two."

Staff Writer Libor Jany contributed to this report. • 651-925-5041 • 952-746-3283 • 612-673-4438