Police said they arrested a man suspected of killing up to 30 older women in two waves of unsolved strangulation-rapes that terrorised Los Angeles and other communities in the 1970s and 1980s.

Detectives of the Los Angeles Police Department's "cold case" unit said John Floyd Thomas Jr, 72, the man they now believe to be the "Westside Rapist," was linked by DNA evidence to five slayings, two with which he is formally charged.

Police said Mr Thomas was a suspect in as many as 25 other unsolved killings.

"When all is said and done, Mr Thomas stands to be Los Amgeles' most prolific serial killer," LAPD detective Richard Bengston told the Los Angeles Times.

Thomas had worked as a state insurance claims adjuster since 1989, the year the second wave of slayings stopped, the newspaper reported.

Held without bail since his March 31 arrest, Mr Thomas is to be arraigned May 20 on two counts of murder in connection with the 1972 slaying of Ethel Sokoloff, 68, and the 1976 killing of Elizabeth McKeown, 67. Both women were also raped.

Since no death penalty existed in California at the time the crimes were committed, Mr Thomas faces a maximum penalty of life in prison without parole if convicted.

The wave of sex crimes was noticed in the early 1970s when a killer began creeping into the homes of mostly older women who lived alone on Los Angeles' west side. The assailant raped them and then squeezed their necks until they passed out or died. Seventeen victims were found with pillows or blankets placed over their heads. At least 20 women survived, but conflicting descriptions of their assailant confounded efforts to identify him.

The LAPD said Mr Thomas was already a convicted felon, having served 12 years in prison for various burglaries, many involving sexual assault. The Times said he also was convicted of a 1978 rape and went to prison for that crime until 1983, coinciding with the period between the two waves of unsolved murders.