Green River killer Gary Ridgway has already confessed to the murders of 48 women, but police who are still investigating the case say there could be many more victims.
Three King County sheriff's detectives continue to work on identifying several victims -- there are four that Ridgway has confessed to killing that they have not identified.
In 2003, Ridgway confessed to killing 48 women and girls between 1982 and 1998 in the Seattle area. The deal spared him the death penalty, instead giving him consecutive life sentences for each murder.
The detectives say that every one of Ridgway's victims is important, but the one they are currently trying to identify is especially significant. Investigators believe she might be the first woman Ridgway killed, and she might break the pattern he established of killing women involved in prostitution.
"I had to kill her at the house," Ridgway told detectives in September 2003.
Ridgway knows where he killed her, and he knows he dumped her remains in a ravine.
He told police he thinks it was 1982 or 1983, but the detectives working the case said it could have been years earlier.
"It was like May or March or something like that, it was nice weather and real green outside," Ridgway said in his confession.
But Detective Tom Jensen said Ridgway's memory of the woman was sketchy.
"He told us she was 16 to 20, with long brown hair, thin to medium build. Beyond that, he doesn't remember a great deal about her," Jensen said. But he did remember where he buried the body.
"I don't know which victim it was, but I'm 100 percent sure she's still there," Ridgway said in his confession.
In the summer of 2003, Ridgway led detectives to a shallow grave where they found a handful of bones and three teeth.
Finding out who this woman is and exactly when she turned up missing could put a new spin on the Green River murder case, Jensen said.
A forensic anthropologist told police the bones could have been buried in the 1970s, which is significant because Ridgway swears he didn't kill anyone before 1982.
"If she was not a prostitute and not inclined toward prostitution it could expand the type of victim that we look at," Jensen said.
And Jensen said it could mean that Ridgway killed many more than he ever admitted to.
"Anything's possible," he said.
To try to find out who she was, detectives have shown Ridgway several photos of women reported missing around the time the body might have been buried, but he has yet to recognize any of them, Jensen said.
Jensen said detectives are hoping someone will remember a woman who went missing around that time who fits the general description Ridgway gave them.
ABC News affiliate KOMO-TV in Seattle contributed to this report.