State police, acting on new evidence they have not disclosed, exhumed the body in January and had forensic anthropologists perform new tests.
The suspect is still alive, and police are working toward an arrest, said Schuylkill County Coroner Joseph Lipsett. Until then, investigators are not releasing specifics about how the boy died.
"We're going to keep the cause of death quiet until an arrest is made," said Cpl. Robert S. Betnar, the lead investigator, whom the family credits for the recent progress.
"This (ruling) was one of the most significant hurdles," Betnar said. "Without it being a homicide, technically there's no crime and we couldn't make an arrest."
The motive remains unclear, Lipsett said.
David's body was found in a remote thicket on the edge of town in December 1985, about a half-mile from his bicycle.
A brother, Joseph Reed of Fort Myers, Fla., long suspected foul play and welcomed the renewed interest in the case. He expects Betnar to make continued progress.
"I'm excited," Joseph Reed, 45, said Thursday. "With Mr. Betnar on the case, I'm 100 percent hopeful."
The boy's remains were sent this year to Dr. Anthony Falsetti, a forensic anthropologist at the University of Florida, who spent about a month analyzing them. Two anthropologists who had initially theorized the boy might have succumbed to an undiagnosed case of diabetes now concur with Falsetti's findings, the coroner said.
Reed's father died when he was a toddler, and his mother died in 2001, Betnar said. A sister who encouraged police to pursue the case, Virginia Meadows, died last year.
Schuylkill Haven is about 75 miles northwest of Philadelphia.