Early on the afternoon of Jan. 3, 2001, authorities in the tiny Rocky Mountain outpost of Guffey, Colo., found Carl and JoAnna Dutcher dead from multiple gunshot wounds inside their home.
Immediately, investigators sensed that this was no ordinary crime, yet it would take months for them to unravel the bizarre circumstances that culminated in an unspeakable triple homicide: Was it all a twisted version of the children's game Simon Says?
After discovering the Dutchers' bodies, investigators quickly zeroed in on their 15-year-old grandson, Tony. He had been visiting at the time of the murders, but was nowhere to be found.
Police called the boy's mother, Jennifer VanDresar.
"I just kept saying, 'You have to find my son, he's hurt, you have to find him,'" she remembered telling the police. "Then it came to me ... and I said, 'He's in the fort.'"
The "fort" was a makeshift campground about 100 yards up a hill overlooking the Dutchers' home.
Here, in this place meant for innocent play, investigators would discover another horrific crime scene: Tony's body was found in a sleeping bag, his throat slashed almost to the spine.
Alongside the body lay an unfinished Scrabble game, a clear indication that Tony had not been camping out alone that night.
Tony's mother told police that Isaac Grimes, Tony's one-time best friend, was supposed to be joining her son for a camp-out.
Initially, Grimes denied being anywhere near Tony Dutcher on the night of the murder, saying he hadn't seen him since school let out for Christmas. Eventually, under pressure from his mother to tell the whole truth, Grimes made a shocking confession: He had killed Tony.
Not only did he confess to the murder, but he also told investigators the entire twisted story leading up to Tony's brutal death: The murder was a test of his loyalty to Simon Sue, leader of a bizarre paramilitary cult called the Operations and Reconnaissance Agents, or O.A.R.A., and made up of seemingly harmless high school boys.
In an exclusive interview with "Primetime," Grimes shared the details of his horrible crime -- revealed to police back in 2001 -- for the first time in public.
On New Year's Eve 2000, Grimes's friend -- and fellow O.A.R.A. member Jon Matheny -- dropped off the boys at the Dutchers' remote mountain home. After dinner, Grimes and Tony climbed to the fort.
That's when a night of innocent fun would turn deadly.
"Up at the top of the hill we talked for a while, we played some Scrabble, and then I murdered him," Grimes told ABC News. "He was wrapped in his sleeping bag. I pointed out what I said was a light in the distance that I wanted him to look at and I kept saying, 'Well, no, you're not seeing it.' So I got behind him and I murdered from there."
But what about Tony's grandparents, Carl and JoAnna Dutcher?
Grimes insists that he is not responsible for their deaths. Instead, he says that Matheny returned to the Dutchers' home and shot them. Then the two boys gathered weapons from the house, loaded them in the car and left.
On the drive back from the mountains, Grimes also says Matheny made a phone call to alleged O.A.R.A. ringleader, Simon Sue -- in Canada with his family at the time -- to tell him that the grizzly mission had been accomplished.
"[Matheny said] something like 'He did it' or something like that, referring to me," Grimes said.