Waseca, Minnesota (CNN) John David LaDue cradled the homemade bomb in a tree not far from school. It was summer 2013, and classes were out -- the perfect time to test his explosive.

He lit the fuse.

Nothing.

The teen had used hot glue for his sealing agent. He switched to auto body filler.

The next time, his bomb exploded.

And the next time, too.

The rush grew addicting. Over a span of nine months, he exploded more than a dozen homemade bombs around this small town in southern Minnesota. At a church. A skate park. A shooting range.

The 11th grader was practicing for his master plan: to carry out one of the worst school massacres in U.S. history.

"I had fun entertaining the thought of actually, like, injuring and maiming people," he told police, "and, like, showing people that I am dominant over them."

His explosives were known as crickets, made from emptied-out CO2 cartridges and filled with gun powder. Police say it's not unusual for teens in rural areas to play around with them. Yet those who study mass killings know their significance: Eric Harris and Dylan Klebold carried dozens of crickets with them when they entered Columbine High School on April 20, 1999.

LaDue had done his homework.

He purchased a black duster jacket so he could dress like Harris. "Kinda want to pay tribute to him," he would later tell police. He hoped to time his attack to the Columbine anniversary, in honor of his idol.

He'd studied the Boston Marathon bombers. He thought their attack weak because they killed just three.

He planned to fill two pressure cookers with 6,000 ball bearings, as well as buckshot and screws. Each bomb would have cans of WD-40 strapped to it to magnify the blast. He would use flash powder, instead of black powder, to create a more powerful explosion than the ones in Boston.

John LaDue enjoyed playing the guitar before his arrest.

He believed Adam Lanza was a coward for killing first-graders. "I wanted to target people in my grade who I knew."

He named five students at his high school who he wanted to kill for specific reasons. Two were classmates who talked too much in German class and "got annoying." A third called him queer on the school bus in seventh grade. He also would target the school resource officer.

So meticulous was his plan that LaDue told authorities he chose a bolt-action Soviet-style SKS rifle to use in the attack -- a weapon without a large magazine like Lanza's AR-15 or other semi-automatic rifles used in shooting sprees.

That way, he said, people lobbying for gun restrictions after his attack would have a weaker argument. "I kinda wanted to prove that wrong."

The pressure-cooker bombs were to be hidden in recycling bins in the hallways at Waseca Junior & Senior High School. LaDue planned to detonate them remotely. He'd use his SKS rifle and a sawed-off shotgun to mop up the rest, before getting killed in a shootout with police.

He hoped his assault would leave at least 40 dead -- more than triple the 13 killed in Columbine.

His plot was thwarted on April 29, 2014, when a 911 caller reported seeing someone she suspected was breaking into a storage locker.

The case looked like a slam dunk. Bomb-making material in the storage locker. A confession. An arsenal in his bedroom.

And a diary he kept to "explain after I was dead why I did it."

But the case would turn out to be anything but simple. And the judicial system would wrestle with this question:

What is justice in a case like this -- a massacre that never happened?

Where does preparation end and a crime begin?

Every few months, you read it or hear it on the news: a "Columbine-style plot" is foiled.

The suspects are almost always white male teenagers who have studied the Colorado high school massacre or cite the killers as inspiration.

In the 16 years since the attack in Littleton, Colorado, more than 40 people have been charged with Columbine-style plots, according to searches of news accounts. Of those, more than a half dozen have come since LaDue's arrest in April 2014.

Perhaps the most lasting legacy of Columbine, says Dr. E. Fuller Torrey, is its allure to disaffected youth. "Eric Harris presented himself as an anti-hero, not as a crazy man. He is easy to associate with if your life is going nowhere," says Torrey, a research psychiatrist, best-selling author and founder of the Treatment Advocacy Center, which advocates for timely treatment of the severely mentally ill.

"They're attracted because [Harris and Klebold] went after the people who were most bothersome to them at that time -- and that's their peers who are not appreciating their 'greatness.' It's not just parents. It's not just society. It's actually getting back at the girls who won't go out with them, the boys who exclude them from peer groups."

JUST WATCHED Teen who plotted to blow up school to get treatment Replay More Videos ... MUST WATCH Teen who plotted to blow up school to get treatment 02:17

In 2013 alone, the FBI said its Behavioral Threat Assessment Center prevented 148 mass shootings at schools, workplaces and other public spaces -- up 33 percent from the previous year.

Experts say the public has gotten better at notifying authorities of suspicious activity.

In Waseca, police Capt. Kris Markeson held a news conference two days after LaDue's arrest and praised the resident who called police.

"This case is a classic example of citizens doing the right thing when things seemed out of place. By doing the right thing," Markeson said, his voice cracking, "unimaginable tragedy has been prevented."

In places like Newtown, Connecticut, and wherever schools have been violated, traumatized families would do anything to trade places with the people of Waseca.

Yet the truth is that after the plots are foiled and the arrests made, the legal system struggles with how to deal with the accused, especially juveniles. Often, the public never learns their names -- or the outcome of their cases. The information is shielded in juvenile court.

When children under the age of 18 are charged as adults because of the seriousness of the threats, punishments range widely from state to state. Courts must decide where preparation ends and a crime begins. The outcomes often depend on whether a prosecutor holds a tough-on-crime stance or is sympathetic to defendants suffering from mental disorders.

A 17-year-old boy with underlying mental health issues was sentenced to 12 years in prison for a 2009 plot on Landstown High School in Virginia Beach, a foiled attack that was timed for the 10th year anniversary of Columbine. The prosecutor in that case was outraged over what he felt was a lenient sentence.

That same year, a 15-year-old boy in Monroe, New York, had a plan to attack his school; he got 18 months in a psychiatric center.

LaDue was 17 but prosecutors vowed to try him as an adult. He faced 12 felony charges: four counts of first-degree attempted murder, six counts of possessing explosives and two counts of attempted criminal damage to property. If convicted on all charges, he faced more than 60 years in prison.

Stephanie LaDue collapsed shortly after her son's arrest: "We were taken from this idyllic little world we'd been living in to just complete utter chaos."

'This was his little surprise for us'

A photograph of a smiling young John and his sister, Valerie, rests on the center of the mantle in the living room. A framed print of the Last Supper stares down in the nearby dining room.

A white basket contains more than 60 letters from strangers who wrote to lend their support to the family. David and Stephanie LaDue have read every note. Each brought solace in the face of Facebook posts from people calling for their son to be dismembered or people who drove by to gawk at their home. One man banged on their door and screamed, "Not in my f----ing neighborhood."

"We were taken from this idyllic little world we'd been living in to complete utter chaos," says Stephanie, who works as a substance abuse counselor.

Within a week of their son's arrest, she collapsed under the stress and checked into a psychiatric facility. She literally had to learn how to walk again.

Feeling alone, she called the mother of one of the Columbine killers. She doesn't want to say which one, but the conversation helped her cope and gave her strength. Yes, her son harbored terrible thoughts, but he didn't harm anyone -- and he was still alive.

The LaDues found themselves facing the question asked repeatedly after mass shootings: How could two parents active in their son's life not know he was plotting such destruction?

David wracks his brain for missed clues. "If you just start from here, it sounds like a kid who never should've been born. The fact that he kept it from us and that this was the way we discovered it was real painful.

"This was his little surprise for us."

Adds Stephanie: "One of the things I remember him telling me in those first weeks was: 'I just felt like something was pressuring me to do it.' I'll always remember him saying that."

She flips through photo albums that capture life "before." Here's John at a zoo. In a baseball uniform. Perched with his sister on their father's back, riding "horsey." He was a good student in high school; he made As and Bs. He wasn't the most popular kid, but he wasn't the most aloof, either. He was never disruptive or violent.

A photograph of John LaDue and his sister, Valerie, rests on the mantle in the family's living room.

At home, he got along with his parents, and his sister. "They're good parents," he told police.

Yet he planned to kill all three. He would then set a fire in town to distract authorities before carrying out his massacre at the school.

Behind bars, John was diagnosed for the first time with a highly functional form of autism spectrum disorder, with violent ideations. Psychologists found that it didn't manifest until late adolescence, and that he was able to conceal his troubles from family, friends and classmates.

Research has shown that people with autism spectrum disorder are no more likely to be violent than the rest of the population. A 2008 review found that 84% of violent offenders with autism also had an underlying psychiatric disorder at the time they committed the crime.

The LaDues don't believe their son was capable of carrying out the attack.

Says his father: "What would you do if you got caught in the darkest moment of your life and thinking the most hideous thing possible -- and everybody knew about it?"

If anything, they believe their son was prevented from killing himself. "I don't think he could've killed us, though he says he wanted to," David says. "I don't ever see that he could've done that."

He does not deny the seriousness of his son's plot, but he's frustrated by how events played out. Police questioned John for three hours before notifying the parents. They'd been texting him for hours, worried something bad had happened. When police arrived, their hearts sank: They thought John had been killed in a car accident.

Police found seven guns in John's bedroom: two near his bed and five in a safe in his closet. All but one of the guns belonged to his father.

David had taught both his children how to hunt and took them to gun safety courses. He trusted his son with guns to protect the family while he worked the overnight shift at a steel plant.

He had no idea that John had purchased a gun; he got it through a friend's dad by forging his own father's signature.

John's sister, Valerie, knew about her brother's fascination with explosives, but she viewed it like any big sister might: My brother is such an idiot. She says she didn't know about his plot. He bugged her about getting a storage locker, saying his room was getting crowded and he wanted to move some stuff. She thought it was a weird idea and refused to help him. A friend's mother did.

Valerie LaDue remembers her brother as her math tutor and the guy who carried her around on piggy back.

Valerie was a senior at the high school and had to return to the very building her brother planned to blow up.

What was her reaction when she heard about his plan, beginning with her assassination?

"It's kinda like, 'Come on, John.'"

Looking back, she believes her brother was crying out for help. "He was trying to put his hand up and say, 'Notice me. Somebody stop me.'"

In his recorded police confession, John LaDue told police he believed he was mentally ill.

"Like when would be the best time for me to see a psychiatrist?" he asks toward the end of his second major interrogation.

Moments later, he adds that he thinks he might be a sociopath. "I don't know," he sighs.

David LaDue describes what he now realizes was a sign of trouble in his son in the months leading up to the arrest. He calls it "The War Within John."

His son had questioned the validity of God and proclaimed himself an atheist. The father sat him down and spoke about the mysterious ways in which God works. He told his son that he too struggled to believe in a higher power when he was young.

"I got there the hard way," he told his boy.

He prayed for God to intervene in his son's life.

Resting in the recliner where he sat the night police raided the home, David recalls a dream he had just days before the arrest:

John was a little boy. Father and son sat beside each other on the ledge of a five-story building. Dad sensed something wrong. A dark force tugged at them. His son asked to climb in his lap, even begged, but Dad told his boy to sit still. To stay put.

Dad looked around to gauge what was happening. Suddenly, his son fell. Down, down, down. The father watched. Helpless. He sprinted down a stairwell.

John smashed onto a patio. He was still breathing, but his body shattered.

David LaDue weeps.

He has seen his son shackled over the last 17 months, his family humiliated, the town of Waseca embarrassed.

But he believes his prayer was answered. That God intervened.

"Divine."

That's his one word explanation for all that has transpired.

The case falls apart

If there was a "war within John," as his father says, there was a war about John going on in the legal system.

The prosecution lost the first battle when a judge threw out the charges of attempted criminal damage to property and the toughest charges: attempted murder.

There was no proof, he ruled, that LaDue would act on his plans to carry out a bloodbath -- a decision upheld by the state appeals court.

"He did not engage in anything more than preparation for the commission of the crimes," the state appeals court ruled earlier this year. "The law in Minnesota does not prohibit [LaDue's] conduct. We cannot invite speculation as to whether the acts would be carried out."

David LaDue says too much time has been spent on his son's comments, which were ruled not criminal.

Suddenly, it seemed, the boy who dreamed of becoming infamous, like the Columbine shooters, was instead a mere footnote, an asterisk to a foiled plot.

He turned 18 behind bars while lawyers, judges and psychologists tried to figure out what to do.

The prosecutor wanted to try him as an adult on the six remaining counts of illegal possession of an explosive device. On June 30 of this year, a hearing was held on the matter. Three psychologists testified.

One had met with LaDue at the request of his parents. Dr. Mary Kenning said the young man scored a 99 percent "amenability to treatment" rating, and that he was at low risk for violent re-offense.

He also received high marks from the detention center for doing "anything we ask without hesitation."

"He has been very steady and stays on track very well," wrote corrections program director Brad Bengston in a June progress report. "He has had no outburst or any disciplinary room time. He has had appropriate behaviors and kept his attitude as upbeat as possible."

That assessment stood in stark contrast to the conclusions of two court-appointed psychologists. They agreed that LaDue would need years of intensive treatment to ensure he's no longer a danger to society.

Beginning around 2013, they said, he had begun fixating on violent images of death, spending about five hours a week watching videos of murders, autopsies and other gruesome scenes. They also said he showed no remorse for his plot.

Dr. Katheryn Cranbook expressed concern over his "lack of insight into the seriousness of his issues and his need for intervention."

Without years of specialized treatment, she said, LaDue "would likely return to his prior fixated interest in violence and would be at significant risk for engaging in acts of serious violence."

Dr. James Gilbertson described five important risk factors that LaDue needed to work on in therapy: how to get along with others; deal with his grievance-oriented thinking; abandon his focus on violent retribution; cope with his inflexible and rigid thinking; and address his secret, isolationist lifestyle.

If those issues are not dealt with, Gilbertson said, then LaDue "represents a substantial probability of being at risk for future violence."

If the court were to treat LaDue as a juvenile, Cranbrook and Gilbertson noted, there wasn't enough time for him to get appropriate treatment even if it were to continue to age 21 under Minnesota's extended jurisdiction juvenile program.

JUST WATCHED Why high school bomb plotter didn't get jail time Replay More Videos ... MUST WATCH Why high school bomb plotter didn't get jail time 03:13

In weighing the matter, Waseca County district court judge Robert Birnbaum noted the Catch 22.

If LaDue were considered an adult, the judge determined, he might not get any mental health counseling while in prison because it is voluntary.

He "would likely finish his time and not have his therapeutic needs met," Birnbaum wrote after the hearing. "He would also be at risk to come out of prison with hardened anti-social beliefs and attitudes as a result of exposure to other inmates."

Lost amid the legal arguments was LaDue.

He did not testify during the hearing, and he declined through his attorney and his parents to speak with CNN. But his family shared hundreds of pages of journal entries he'd made while in detention. In an entry dated June 27 of this year, he broached the subject of his arrest.

"The choices I've made that got me in the justice system were based off of selfish and lazy choices. They were also the result of lack of concern for what may go wrong," he wrote. "I have made a decision to act responsibly and to stop engaging in illegal behavior. I am finished with an irresponsible lifestyle. I'm ready to make my plan for action.

"I believe that if I stay as I currently am that I will be able to have a very productive lifestyle and accomplish things I've always wanted to."

His hope: to become a mathematician.

A chance at redemption

The young man stands in the courtroom and raises his right hand. With his black-rimmed spectacles, he looks more like a schoolboy from Harry Potter than the shooters at Columbine High School.

John David LaDue is escorted to the Waseca County Courthouse for his sentencing hearing.

On this September day, 17 months since his arrest, LaDue pleads guilty to a single felony count of illegal possession of an explosive, closing the books on a criminal case more notable for what it is not.

All other charges have been dropped in a plea deal the prosecutor and defense believe benefits both LaDue and the public.

By accepting the plea, LaDue avoids prison time and will receive up to 10 years of court-ordered treatment for autism spectrum disorder. If his treatment is successful, he will move into a halfway house or transitional treatment facility before being reintroduced to society under intensive supervision.

He cannot have contact with his old school. He must be "law-abiding and of good behavior in all respects." The goal is to get him as much treatment as possible until he turns 25, the age at which psychologists say the adult male brain fully matures.

Waseca County Attorney Brenda Miller stands by her prosecution, saying in a written statement that the original charges "best reflected the planning and actions he undertook in anticipation of his final goal: killing his family, killing the school liaison officer, bombing the Waseca Junior & Senior High School and killing as many students as possible."

When the most serious charges were thrown out, Miller said, "gone also was any possibility of a long prison sentence."

"It is our belief that this plea offer is the best outcome possible, under the circumstances, to ensure public safety."

After a year and a half, this is what justice looks like in a foiled plot for a disaffected youth in Minnesota.

The hearing ends and the court clears. Escorted by bailiffs, LaDue begins to walk out, then pauses and leans against a banister.

Looking at him, I can't help but remember one of the letters of support his family shared with me. It was addressed to John, and written by a 22-year-old woman from Russia named Victoria.

"I was just like you in my teenage years," she wrote. "I don't have a lot of feelings that most people have." She felt isolated and studied the Columbine killers. "By the age of 16, I knew the name of almost every person who committed similar crimes that Eric and Dylan did..."

But she turned a corner and never acted on her darkest thoughts.

The thing that distinguishes you from the Columbine shooters, she wrote, is "the fact that they committed gruesome crimes and they can't change that.

"You're really the lucky one. You have a chance they never had. And you should use this chance."

LaDue recently earned his high school degree, finishing with a 3.3 GPA at the detention center where he was held for most of the last year. He was valedictorian of his class of 13.

His next stop is a treatment facility in suburban Atlanta -- if Minnesota figures out how to pay for his care and Georgia accepts his transfer.

If he meets the court's demands, the single felony charge to which he plead guilty will be knocked down to a misdemeanor and wiped from his record.

As if this never happened.