Now authorities believe they have a key piece to the puzzle: A 1969 Camaro, just like the one the teens were driving, was pulled from a lake with the skeletal remains of three people inside.
But that wasn't the only discovery. A second car containing remains, an early 1950s Chevrolet, was also recovered from Foss Lake. Custer County Sheriff Bruce Peoples believes it may solve another case in which two men and a woman disappeared a year before the teens vanished.
"These vehicles match those missing-persons reports real close," Peoples said Wednesday as investigators combed through what remained of the rusty, mud-covered vehicles.
Both vehicles were discovered Tuesday in about 12 feet of water by divers conducting a training exercise at the lake. The vehicles were only about 50 feet from the end of a boat ramp near a marina, but Peoples said it was no surprise that the murky waters held a secret.
"This lake isn't crystal clear. It's a typical western Oklahoma lake with a lot of silt in it. The visibility is only 6 to 12 inches on a good day," Peoples said.
While Peoples said he was confident the Camaro held the remains of the three teens, the origins of the bones in the second vehicle were less clear.
Tim Porter said he believed the remains could be those of his grandfather, John Albert Porter, who disappeared along with two others in 1969.
"Forty-something years of wondering who or why," Porter said. "If it is my grandfather in there, it's a gift."
The sheriff said Wednesday he was not sure whether the cars held the remains of five or six bodies. The state medical examiner's office believed the remains of six people were recovered.
The bones were sent to the medical examiner's office for identification and to determine the cause of death.
Divers had found three skulls as of Tuesday evening. They planned to continue looking for more remains, said Oklahoma Highway Patrol spokeswoman Betsy Randolph.
Authorities hoped the discoveries offer some relief to families who may have gone decades wondering about the fate of a missing loved one.
"We're hoping these individuals, that this is going to bring some sort of closure to some families out there who have been waiting to hear about missing people," Randolph said. "If that's the case, then we're thrilled."