Three Grayson High School teenagers were riding the bus to school Dec. 17 when they hatched a plan to rob a classmate who collected expensive basketball shoes, a Gwinnett County police detective testified Friday.

Two days later that classmate, 14-year-old Paul Sampleton, was dead — killed by three bullets to the head during a robbery at his Snellville townhouse that unfolded the same day as the trio had planned. Sampleton was bound and killed in his kitchen just minutes after he arrived home on Dec. 19 following early release from school for the holidays.

The three teenagers, Larnell Sillah, 15, Achiel Morgan, 15, and Romaine Stewart, 18 — all of whom are being charged as adults — are alleged to be active members of a street gang called the Young Wavy Goons.

Each would later recount in separate interviews with police that they had planned some details of the robbery during a conversation on the bus, Gwinnett County Police Homicide Detective Andrew Whaley testified at a preliminary hearing for the boys on Friday.

They allegedly agreed Morgan and Stewart would intercept Sampleton as he approached his house. They would create a diversion by engaging him in a fight while Sillah snuck inside Sampleton’s home and snatched the 14-year-old’s valuables, Whaley testified.

The teens went so far as to feign friendship with Sampleton, who played on the freshman football team with Morgan, in the days leading up to the robbery. They invited him to Stewart’s house to get a haircut so they could follow him home afterward and get his address, according to Whaley.

“They said they were gonna rob him for his shoes,” Whaley said. “That was the main focus.”

Gwinnett County Magistrate Judge Phil Wiley found probable cause to bind over to Superior Court a murder charge against the suspected triggerman, Sillah, and armed robbery charges against Morgan and Stewart for allegedly helping to plan the robbery.

However, according to Detective Whaley’s testimony, Morgan and Stewart did not participate in the actual holdup. Instead, police believe Sillah, the alleged leader of their gang, went to Sampleton’s house accompanied by other helpers.

Three flatscreen televisions, an Xbox video gaming system, a computer, headphones, an iPad2, clothes and eight pairs of shoes were stolen from Sampleton, the detective said.

Whaley also said there is a “person of interest” in the slaying, but no warrant has been issued for his arrest.

The vehicle suspected of being the getaway car in the case, a silver BMW, is registered to the person of interest. A vehicle of the same description was linked to a road-rage incident in Norcross in which shots were fired but no one was injured a few hours after Sampleton’s robbery.

Defense attorneys have pointed to the lack of witnesses of the school bus conversation as evidence of their clients’ innocence, and emphasized that no one saw the three boys near the victim’s home on the day of his murder.

The murder weapon also has not been found.

However, a pair of Sampleton’s shoes were found in the garage of the house where Sillah lived.

Sillah’s defense attorney, Tom West, said his client is not guilty. “And I think the police know that.”

“There is a whole lot of speculation and very little, if any, evidence that my client was involved in this at all,” West said.

Sillah and Morgan were being housed in a juvenile detention facility, while Stewart is at the Gwinnett County Detention Center. All three were being held without bond.