Aug. 18, 2009— -- How far could an innocent high school student go to try to fit in? In a bizarre case in Colorado, the answer appears to be all the way to murder.
Isaac Grimes is serving a 60-year sentence for killing his onetime best friend Tony Dutcher when he was only 15. Grimes pleaded guilty to second-degree murder, but the most shocking part was his explanation of why he did it. According to him, it amounted to a twisted version of the children's game Simon Says.
It all began in the fall of 1999, when Grimes entered his freshman year at Palmer High School in Colorado Springs, Colo. He was a lonely boy, who admits he was not popular.
"I wasn't a people person," he said.
His parents, Rob and Donna Grimes agree.
"It was like he was set apart, and he didn't relate as much to kids his own age. He read. Read lots and lots," said Donna.
But early in that fateful year, he crossed paths with a charismatic high school senior named Simon Sue. The unlikely pair shared an interest in chess and video games, and with that, the upperclassman took the younger, nerdy boy under his wing.
Grimes said Sue even offered him a chance to join his club called the O.A.R.A., or the Operations and Reconnaissance Agents. It would be the turning point of Isaac's life. For a young boy, desperate to have connections with others, hanging out with Sue and being invited to join the O.A.R.A was everything he desired -- at first.
"It was a lot of compliments -- a lot of self-esteem building material. Like you're one of us -- you're cool. You're part of the group," he told "Primetime".
Grimes said he finally felt like he was part of a "band of brothers." Sue reassured him that the group of boys, which included fellow high schoolers Jon Matheny and Glen Urban, would look out for one another.
As much as they wanted their son to have friends, Grimes' parents were skeptical of the relationship.
"One time I had said, 'you know, Simon's a senior -- why is he hanging out with you?' And he said because 'I'm smart,'" recalled Donna, who is convinced Sue preyed upon her son's vulnerability. "It's a shark in the water thing, they smell blood, and I think Simon smelled blood."
She couldn't have imagined that her worst fears — and then some — would soon be realized.
Teen Says He Was Forced to Murder
Cathleen Mann is a national expert on cults. She readily applies this label to Sue's O.A.R.A. She has interviewed Grimes many times and helped his legal team as they strategized his defense.
"[Grimes] didn't know he was getting involved in a cult, of course," explained Mann. "This is the way that all these groups work, is they get you emotionally invested and then they start to disclose their inner purposes. And by the time you figure out what's going on, you're involved."
Grimes and his so-called band of brothers would quickly move on from fun, harmless activities, like chess to much more dangerous ones. Grimes claims that Sue took the boys to a local range to practice shooting weapons, and he taught them how to disassemble and clean the firearms.
The group was organized in a paramilitary structure with Simon in command. "I started out as a lieutenant, and then became a major, and then a lieutenant colonel," Grimes said.
Grimes also says he was forced to eat and drink until he vomited and that he had to repeatedly watch "Faces of Death," a notorious cult film featuring gruesome footage of animals and humans being killed.
This was all part of Sue's master plan, says Grimes.
"I think that it desensitized me to violence," he said. "I had been trained into obedience like a dog at heel. Going against him would be like going against, living basically, to me, just an alien thought."
All of this was supposed to be part of their training in preparation for their larger mission: To be prepared to fend off a coup in the Sue family's native land, the small South American country of Guyana.
Coincidentally, this tiny country is perhaps best known to Americans for another cult tragedy, the mass murder-suicide of People's Temple leader Jim Jones and 918 of his followers.
When asked now if he ever thought that claim was crazy -- that the idea of a team of 15-year-olds going to fight in a foreign war was ridiculous -- Grimes said, "No, I think I should have!"
Unlike this dubious geopolitical scheme, Grimes' motivation was simple and personal. His goal was "to have friends, to be part of something bigger, something good."
Unspeakable Murder of Former Best Friend Was Loyalty Test, Says Killer
Grimes claims he missed possible warning signs partly because he was under tremendous pressure. He maintains that Sue had essentially been brainwashing him.
"He believed that he would be killed. Now, whether that makes common sense or not is not really relevant. What's relevant is that he believed this and that all members of these kinds of groups believe things that we don't understand. This is the byproduct of indoctrination," explained Mann.
Grimes said he was ordered to do many things he did not want to do -- including burglary -- but was convinced if he did not follow Sue's orders, he and his family would be killed.
He not only believed that Sue would take action against him and his loved ones, but that the O.A.R.A. was a global organization that infiltrated into local law enforcement.
Grimes claimed that Sue had him make copies of the keys to his home and provide Sue with pictures of his entire family so he could identify them.
He said he lived in constant fear. "I remember being very afraid that he was always watching me. I used to go to the bathroom with the lights off, because I thought someone might be watching me," said Grimes.
"He had me bring pictures of my family for him, for him to send to his superiors, so that they would know who to kill," Grimes told ABC News.
He was convinced there was no escape -- no way to tell his parents, no place where he could run for protection from what was happening to him.
So when Sue ordered Grimes to "prove his loyalty" by not just committing murder, but by killing his former best friend, Tony Dutcher, and his family, the younger boy readily agreed. In this case, Simon Says was no childhood game.
On New Year's Eve 2000, Grimes viciously sliced Dutcher's throat, nearly decapitating him in the process. Dutcher's grandparents, Joann and Carl Dutcher, were also found shot to death in their home.
But as details about the case and Simon's bizarre group began to emerge, the truth about this unspeakable crime grew even murkier. Could it be that Grimes was the real mastermind and Sue was another victim?
Visit the "Primetime" site Wednesday for Part II of the story.