LOS ANGELES (AP) – Police believe a 72-year-old insurance claims adjuster arrested earlier this month is the most prolific serial killer in the city’s history, having raped and strangled as many as 30 older women over two decades.

The break in the cold case came in October when John Floyd Thomas Jr., who had twice been convicted of sexual assault, had a DNA sample taken as part of an effort to build an offender database.

Thomas was charged April 2 with murdering one woman in 1972 and another in 1976. DNA matching Thomas’ was found at three other crime scenes in the 1970s and ’80s, police robbery-homicide Capt. Denis Cremins said.

Detectives now consider Thomas a suspect in at least 25 other killings, and the number could grow as detectives probe unsolved cases going back to the 1950s, Cremins said. It could not immediately be determined where the other killings took place.

“If he turns out to be the guy, he probably would be the largest ever (serial killer) in the city of Los Angeles,” Cremins said.

Thomas was sentenced to six years in 1957 for burglary and attempted rape in Los Angeles. Two parole violations sent him back behind bars until 1966.

In the first wave of killings in Los Angeles in the mid-1970s, a man police dubbed “The Westside Rapist” entered the homes of dozens of elderly women who lived alone, raped them and choked them until they passed out or died.

During that time, Thomas was a social worker, hospital employee and salesman. The attacks stopped in 1978 – the year Thomas 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, including five slayings in the nearby Los Angeles County town of Claremont.

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.

Investigators said the attacks stopped in 1989, when Thomas began working at the State Compensation Insurance Fund in Glendale. He was arrested at his South Los Angeles apartment on March 31.

“As far as why he stopped, we don’t know for sure if he stopped,” Detective Rick Jackson said. “Who knows? It could be age-related, we just don’t know enough about him at this time.”