Updated

Washington state authorities said they have positively identified the remains of a woman killed by the Green River Killer, one of the nation's most prolific killers.

The King County Sheriff's Office said Monday that remains found in Auburn, Wash., in 1985 belong to Sandra Denise Major.

The 20-year-old was reported missing on Dec. 24, 1982, and was last seen getting into a pickup in North Seattle.

Relatives in New York state had already assumed that she had died at the hands of Gary Ridgway, just like dozens of prostitutes who worked in the Seattle area in the early 1980s.

But it wasn't until April that Major's cousin called the King County Sheriff's Office after seeing a Lifetime channel movie about Ridgway, who was dubbed the Green River Killer because he dumped some of his victims in or along a river that runs through King County.

It was the first time anyone from the missing woman's family had reached out to law enforcement, sheriff's Detective Tom Jensen told The Seattle Times (http://bit.ly/LvpQXM).

"He knew his cousin had come out here in '82," said Jensen, a longtime member of the Green River Task Force. "He said she was involved in prostitution and she disappeared."

Police in Rochester, N.Y., collected DNA samples from the Major's two brothers and sister, and the National Center for Missing and Exploited Children asked the University of Texas Center for Human Identification to speed up the testing, authorities said. Results showed that DNA of the remains matched the family's DNA.

Ridgway has admitted to killing Major and 48 others. He is serving a life sentence at the Washington State Penitentiary in Walla Walla.