The discovery was made on Dec. 21 by three teenagers who were playing in a wooded ravine in Auburn, near Seattle.
"We had to go over a log and it was slippery," Skye Hagan told NWCN.com. "I kind of fell and came face to face with a human skull."
The boys notified the Auburn Police Department, which confirmed that the remains were human and turned the investigation over to the King County Sheriff's Office. Additional bones were later located at the bottom of the ravine, police said.
A forensic odontologist has since positively identified the skull found in the ravine as that of Rebecca "Becky" Marrero, a 20-year-old woman who investigators have long suspected was a victim of Ridgway's.
"With the discovery of Ms. Marrero's remains, detectives and prosecutors will now review the investigation into her disappearance and death," the King County Prosecutor's Office said in statement to the media. "Investigators will examine all aspects of the case including any potential involvement of Ridgway."
Ridgway, 61, was arrested in November 2001, after DNA evidence conclusively linked him to four unsolved homicides. Additional victims were later added to the indictment. The media dubbed Ridgway the "Green River Killer," because his first five victims were found in the Green River in King County.
In 2003, Ridgway was spared the death penalty when he entered into a plea agreement with prosecutors. Per the terms of that agreement, Ridgway pleaded guilty to 48 counts of aggravated first-degree murder and agreed to cooperate in locating the remains of additional victims.
In his confession, Ridgway acknowledged that he targeted prostitutes because they were "easy to pick up" and said he hated most of them.
"I killed so many women, I have a hard time keeping them straight," Ridgway wrote in a statement for the court.
For his crimes, Ridgway was sentenced to 48 consecutive life terms in prison.
For the past seven years, Ridgway has kept a relatively low profile at Washington State Penitentiary in Walla Walla. The discovery of Marrero's remains, however, has again thrust him into the spotlight and resulted in renewed interest among investigators.
Marrero was last seen on Dec. 3, 1982, leaving a motel near Seattle-Tacoma International Airport. For 27 years, her family was left wondering what happened to her.
"She came back for Christmas in December, which is a blessing," Marrero's younger sister, Mary Marrero, told KING 5 News. "She left in December; she came back in December."
According to the Seattle Post Intelligencer, the location where the remains were found is in the same general area where authorities discovered the remains of Marie Malvar in September 2003. Malvar, a 17-year-old prostitute, was murdered by Ridgway in April 1983.
Ridgway was questioned during taped confessions in 2003 about Marrero's disappearance, but he was unable to provide enough details about her case to convince police he was culpable for her death. Consequently, she was left out of his plea agreement. As a result, prosecutors could now decide to charge him with an additional count of capital murder.
"This case was discussed, he disclosed as much as he could. I like to think it's not something new that's going to reopen those possibilities," Prothero said.
However, Mary Marrero told KING 5 News that investigators are confident they can make a case and are holding her sister's remains as evidence.
"Hopefully [he will be] given the death penalty," she said.
The King County Prosecutor's Office said it will review all the evidence and announce its decision "at a later date."