GREENCREEK, Idaho (CNN) -- It was just 2½ years ago when Elaine Sonnen found out that her 16-year-old son, Richard, had been planning a Columbine-style attack at his high school.



Richard Sonnen spent 16 months in mental health institutions after plotting to kill his high school classmates.



It would be a fitting payback to his high school classmates who Richard said relentlessly bullied him.



"I always wanted to get back at them," Richard Sonnen said of his classmates. "I always wanted to strangle them. ... I was always mad. I was always angry and I would come home and cry to mom and dad."



Both Richard and Elaine Sonnen spoke to CNN at the 45-acre family farm.



Unlike  Columbine and recent school shootings at Northern Illinois University and Virginia Tech, Elaine Sonnen did see the warning signs in her son and was able to stop him.



Elaine and her husband, Tom, adopted Richard from a Bulgarian orphanage when he was just 4½ years old.



"I mean, we just loved him, and he was just a big sparkle of life," she said.



But only a few months after they brought him home, they began to see another side of their son. He was angry and unpredictable.



Elaine Sonnen says that at age 6, Richard told her he wanted to kill her. She said he would shake with anger to the point that he'd scream at her, telling her he wanted to destroy her.



"People thought he was just the greatest kid in the world. Very polite, well-mannered, caring," Elaine Sonnen remembered. "At home, he could be anywhere from just a really helpful kid to a monster. A terrifying monster."  Mother says son had 'two' personalities »



In junior high, he said, "evil" classmates started picking on him. Boys and girls, he said, bullied him until he couldn't take it anymore.



"I always wanted to get revenge," he said.



By the eighth grade, Richard was put on anti-psychotic medications. He had been diagnosed as bipolar and was suffering from obsessive compulsive disorder and other disorders.



In 1999, when the Columbine shootings happened, the Sonnens feared that Richard might do the same thing one day.



"We stopped and looked at each other and said, 'This could be Richard; some day this could be him,' " Elaine Sonnen said.



Years later, during his junior year in high school, they were right.



Fed up with the bullies, Richard says, he felt like an outcast and started looking for a way to get even. Secretly, he began reading books about Columbine in his school library. The shooters, Eric Harris and Dylan Klebold, became his heroes.



"They planned it out so perfectly and so meticulously ... that I just, wow, you know," he said. "They're my gods."  Watch a preview of "Campus Rage" »



He even created a hit list of the classmates he planned to kill at Prairie High School in Cottonwood, Idaho.



"My plan was to set around bombs around the school. ... I analyzed a lot of where everybody sat and where everybody did their thing," he said. "I had pinpoints of where I wanted to go, where I wanted to do it."



Harvard Medical School psychologist William Pollack, who consulted on a 2002 federal government study of school shootings, said it found that most school shooters often had feelings of anger, sadness and isolation as well as homicidal and suicidal thoughts.



"We see a young man who obviously is telling us how depressed he was, how angry he was and how much he looked up to people who we know are very disturbed and very dangerous, and how close he came to killing people," said Pollack, who watched CNN's interview with Richard.



Elaine Sonnen found out about her son's plan during a conversation with him. She ordered him to write down the names of
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