A 72-year-old man is suspected of being a prolific serial killer who raped and killed as many as 30 women in waves of attacks that terrorized Southern California decades ago, police said.

John Floyd Thomas Jr. is charged with two killings, and DNA matching his was found at a total of three other crime scenes in West Los Angeles in the 1970s and Claremont in the 1980s, police Robbery-Homicide Cold Case Detective Richard Bengston said.

Evidence in 25 other killings is being examined, but authorities said they suspect Thomas.

"When all is said and done, Mr. Thomas stands to be Los Angeles' most prolific serial killer," Bengston told the Los Angeles Times in a story published Thursday.

Police planned to reveal details of the case at a news conference.

Thomas was being held in county jail and could not be reached for comment. Officers reached by phone by The Associated Press had no information on whether he had obtained an attorney.

In the first wave of killings in Los Angeles in the mid-1970s, a man police dubbed "The Westside Rapist" entered the homes of elderly women who lived alone, raped them and choked them until they passed out or died. The 17 people killed were found with pillows or blankets over their faces.

A decade later and 40 miles to the east, five elderly women in Claremont were found raped and killed, also with blankets or pillows over their faces.

Despite some 20 survivors, detectives didn't connect the two cases. There were conflicting descriptions from victims, a lack of communication between agencies and an absence of DNA technology.

Thomas, who has twice been convicted of sexual assault, had a DNA sample taken last October as part of efforts to build an offender database.

He was arrested at his South Los Angeles apartment on March 31, authorities said. Soon after, he resigned from his job with the State Compensation Insurance Fund in Glendale, where he had worked since 1989.

He was charged April 2 with the murder of Ethel Sokoloff, 68, in 1972, and Elizabeth McKeown, 67, both in Los Angeles.

Bengston said Thomas' DNA also was connected to the scene of a 1975 Los Angeles murder, a 1976 Inglewood murder, and a Claremont killing in 1986.

Thomas was born in Los Angeles. His mother died when he was 12 and he was raised by an aunt and godmother, attended public schools and joined the Air Force in 1956. He was considered sloppy and late and was dishonorably discharged, the Times said, citing military records.

In 1957, he was convicted of burglary and attempted rape in Los Angeles and sentenced to six years in prison. After his release, parole violations sent him back behind bars until 1966.

A few years later, a series of attacks on elderly women began by the so-called "Westside Rapist," who roamed Los Angeles County from Hollywood to Inglewood.

During that time, Thomas was a social worker, hospital employee and salesman.

The attacks stopped in 1978 — the year he went back to prison for the rape of a Pasadena woman.

After his 1983 release, he moved to Chino in San Bernardino County and took a job as a hospital peer counselor in nearby Pomona. That year, a series of attacks on elderly women began that included five slayings in the nearby Los Angeles County town of Claremont.

Investigators say the wave of attacks stopped in 1989 — the year Thomas began working in Glendale, 30 miles away.

Los Angeles police were still investigating at least a dozen other murders connected to an unidentified serial killer who has been dubbed the "Grim Sleeper."