Gary Ridgway claims to be helping victim's families bring closure in a series of telephone interviews with KOMO-TV's Charlie Harger. Courtesy KOMO-TV

AMERICA'S most prolific serial killer, who is in jail for killing 49 women, has now confessed to a TV crew to killing 80.

Gary Ridgway, known as the Green River Killer, claims he is revealing the true number of his victims to try to help bring closure to their families.

Ridgway, who murdered prostitutes and teenage runaways in King County, Washington State during the 1980s and 1990s, made the revelation in a series of telephone interviews with KOMO-TV's Charlie Harger.

PICTURES: KILLERS, CANNIBALS, VICTIMS

Ridgway, who was arrested in 2001 through DNA evidence, avoided the death penalty by pleading guilty to killing 48 women and was sentenced to 48 consecutive life terms. A 49th victim was later identified and a 49th life sentence was added in 2011.

Ridgway, who was married three times, was a truck painter from Seattle. He admitted picking up prostitutes and teenage runaways, strangling them during sex and dumping their bodies in wasteland near the 105km-long Green River.

Ridgway has previously confessed to US Congressman Dave Reichert, then part of the police task force trying to solve the murders, to killing 71 women. Now he has told Harger that he murdered more.

Harger said that he believes Ridgway's true motivation for agreeing to the interviews is to "up his count" and make it appear that he killed more, with Ridgway now stating he murdered 80 women.

"I think he wants to show the world that, 'Here I am, Gary Ridgway, the truck painter from Kenworth, the guy who everybody thought was slow since elementary school, somebody who couldn't hold a candle to Ted Bundy. But, here I am, and I'm the best at something.'"

Harger despite his reservations believes Ridgway's confessions have to be investigated.

"There's so many people out there who have never been found, so many women dead in the cold," Harger said.

"Maybe if we listen to the clues and cut through his lies, we will find a nugget of truth, the clue investigators have waited for," he said. "It's a chance we have to take."