A weekend hiker found the skull of one of the 48 women Green River serial killer Gary Ridgway admitted murdering in his 2003 plea bargain with King County prosecutors.

The skull of Tracy Winston, who was 19 when she disappeared from Northgate Mall on Sept. 12, 1983, was found Sunday by a man hiking in a wooded area near Highway 18 near Issaquah, southeast of Seattle.

The sheriff's office used dental records to identify the skull, which Detective Tony McNabb said had been placed alongside a dirt road sometime within the past two weeks. No other bones were found at the site.

Investigators are asking whoever moved the skull and placed it where it was found to call the sheriff's department.

Sheriff Sue Rahr said there are no plans to file any criminal charges and that detectives believe additional information could reveal important clues about other killings.

"Gary Ridgway had so many victims, and there are so many things we still don't know — about what he did with the bodies, how he treated his victims," Rahr said at a news conference in her office.

Rahr said the sheriff's office has no reason to believe the 45-year-old hiker who found the skull was the one who moved it.

"Our assumption is that a hiker or a hunter found it and for whatever reason didn't want to call the police and set it alongside the dirt road so somebody else could report it," McNabb said.

Rahr, McNabb and Detective Tom Jensen disclosed few details about the location where the skull was found, saying that doing so might compromise the investigation.

"It's quite some distance from any area where we found any other remains, and nowhere near where he took us," McNabb said, referring to guidance Ridgway gave the sheriff's office as part of his plea to avoid the death penalty.

Detectives believe some of Winston's remains — a dozen or so bones — were found in 1986 at the base of a tree in Cottonwood Park in Kent, south of Seattle. Ridgway admitted killing the woman whose remains were found there, but was "unable (or unwilling) to account for those parts of Tracy's skeleton that were not found," the sheriff's office said in a statement.

Cottonwood Park is near the Green River, about a quarter mile from Peck Bridge, where the body of Wendy Coffield, Ridgway's second known victim, was found in July 1982. It is also within a quarter mile of where six other Green River victims were found.

Ridgway admitted killing 48 women from 1982 through 1998. He's serving 48 consecutive life sentences at the state prison in Walla Walla in the southeastern corner of the state. Four of his victims have never been identified.

Ridgway once said he killed as many as 71 women, according to transcripts of interviews with investigators that were released last year. Almost all of his identified victims were prostitutes or runaways.