09/19/2013 11:06 am ET Updated Sep 20, 2013

Gary Ridgway, Green River Serial Killer, Claims 20 Additional Victims Never Found (VIDEO)

One of the Pacific Northwest's most notorious serial killers has made a chilling new claim about the number of women he killed in the 1980s and 1990s.

Gary Ridgway, a Seattle-area truck painter, was eventually convicted in the murders of 49 prostitutes and runaways who he solicited and then strangled in Washington state's King County, according to CNN.

Currently in jail serving 49 life sentences, Ridgway told local station KOMO News that he killed far more victims than police realized.

"The total number [of victims] is 75 to 80," Ridgway, who's known as the "Green River Killer," said in a phone interview with KOMO's Charlie Harger.

Speaking with Harger, Ridgway said he's coming forward now because he want to help recover the bodies still out there.

“You can’t go back and change the past; it’s over with,” Ridgway told the station. “All we can do is try to make it better.”

While the serial killer protests that he has nothing to hide anymore, Harger told ABC News that he's skeptical.

"The strange thing about Gary Ridgway is if you didn't know the depravity, if you didn't know the evil that this man committed, you would have no clue when you talked on the phone with him," Harger told ABC. "He's playing everybody when he talks... I don't think Gary Ridgway can even comprehend the truth."

Local authorities have also sounded their own note of caution.

"Everyone needs to go in there -- including the press, including these other investigators -- with their eyes wide open," King County Sheriff John Urquhart said, according to the Associated Press. "When you're dealing with Gary, he's going to ramble, he's not going to tell the truth, he's going to play games. Maybe you'll get a nugget out of him; maybe you won't."

The AP notes that if Ridgway was convicted of another murder, he could possible face the death penalty. So far, Urquhart said Ridgway has provided no real information since his conviction.

"I don't think he is capable necessarily of giving good information. But, he still likes to talk about it," Urquhart said.

CORRECTION: A previous version of this article reported that Ridgway was a truck driver. Although employed by a trucking company, Ridgway was a painter, not a driver.