A convicted murderer serving life in prison has been charged with four new slayings, suggesting that at least three serial killers were stalking women two decades ago in South Los Angeles, a prosecutor said Wednesday.

The notorious "Southside Slayer" killings claimed the lives of as many as 90 women on inner city streets at a time when many had turned to prostitution to support crack cocaine habits, authorities said.

"It's pretty mind-boggling that you would have multiple people raping and killing women," Deputy District Attorney Bobby Grace said after 52-year-old Michael Hughes, the latest suspect, pleaded not guilty to murder and sexual assault charges.

The charges were based on "cold case" hits on a DNA analysis computer in Sacramento.

"We weren't looking for him," Grace said. "That's the beauty of the new systems."

Two men were previously convicted in the string of killings in the 1980s and 1990s.

Chester Turner, a pizza deliveryman, was sentenced to death last year for killing 10 women and a fetus. Louis Craine died of natural causes on death row in 1989 after being convicted of strangling four prostitutes.

Police initially thought just one killer was behind the slayings and dubbed him the "Southside Slayer."

"It's been proven now there is not one 'Southside Slayer,"' Grace said.

The prosecutor suggested as many as five killers could have been behind the scores of killings.

"But due to destruction of evidence over the years, the vast majority of these cases will never be solved," he said.

The new case against Hughes involves three women and a teenager killed from 1986 to 1993. Autopsies concluded they were sexually assaulted and strangled.

Hughes was accused in the new complaint of murdering Yvonne Coleman, 15, and Verna Williams, 36, in 1986, Deborah Jackson, 32, in 1993. and Deanna Wilson, 30, in 1990.

Prosecutors have not yet said if they will seek the death penalty.

In 1998, Hughes was convicted of murdering four other women in 1992 and 1993. Authorities did not connect those deaths to the "Southside Slayer" case at the time.

Coleman was a student, unlike the other victims who were women in their 30s with histories of drug use, Grace said.