EUGENE — It's been 25 years since Candice Roy was sexually assaulted and strangled just days before her high school graduation.

EUGENE — It's been 25 years since Candice Roy was sexually assaulted and strangled just days before her high school graduation.

The unsolved case involving the Eugene teenager still bothers one of the first detectives who arrived at the scene. "That's one that's always been really puzzling, and I'd still really like to see someone solve it," former state police Lt. Phil Zerzan told The Register-Guard newspaper in Eugene. "We ran all over the state chasing leads in that case," he said. "It was just one of those where we didn't catch any breaks."

Though the trail has gone cold, investigators say they remain hopeful that someone who knows what happened will come forward and provide key information.

Roy's body was found on June 6, 1988, under a stand of trees four blocks from her home. The 17-year-old had been reported missing by family days earlier.

Investigators questioned dozens of people at the time, including two men who had been arrested in the killing of a 19-year-old Springfield woman just a few days before Roy's death. The men, who are serving life sentences, were cleared of any involvement in Roy's death.

Detectives also used DNA testing — which at the time still was a new investigative tool — and about 35 people provided samples, none of which matched evidence collected from Roy's body. Zerzan thinks there's a chance the killer is, or was, a state prison inmate who could be identified through DNA. But that person might have been convicted before Oregon began requiring felons to submit DNA samples for a state database.

The notion that Roy's killer — or someone else with knowledge of the slaying — might still be behind bars on an unrelated conviction led authorities in 2011 to include her killing among 52 cold cases highlighted in a set of playing cards that state prison officials made available to inmates.

Roy's case is the four of hearts.

Roy's case file, meanwhile, is contained in two large boxes and two shelves inside the state police office in Springfield, Sgt. Andy Kenyon said.

"It's frustrating to not be able to do more with it," Kenyon said.

Roy's mother moved to Canada with her husband not long after her daughter died. Zerzan said he lost touch with her years ago, after the family requested that police leave them alone unless there was a break in the painful case.

"I'm surprised it's been that long," Zerzan said when informed of the anniversary. "But it is coming up on graduation time, and that does always bring up the memory for me."