Police say a 14-year-old boy shot and killed his grandparents during a robbery and murder scheme hatched while he and two other friends were held in a juvenile jail.

Justin Staton was charged as an adult with murder Friday along with 17-year-old Hunter Drexler in the July 22 deaths of Robert and Patricia Cogdell in Conway, Arkansas. Police say the pair shot them and dumped their bodies in a nearby wooded area.

A police affidavit said Staton acknowledged the crimes and that he had told a relative Drexler was involved.

According to the affidavit, a 17-year-old girl who was at the house at the time said something should be done because the grandfather didn't die immediately. Staton walked over to his grandfather and shot him once or twice more.