The official says Rodney Alcala has been indicted on murder charges in the deaths of Cornelia Crilley and Ellen Hover. Crilley was found strangled in her Manhattan apartment in 1971. Hover disappeared in 1977 and her remains were later found on an estate outside the city.
The official spoke on condition of anonymity to discuss an indictment that has not been made public.
The Manhattan district attorney's office is declining to comment. A news conference is scheduled Thursday afternoon.
The 67-year-old Alcala was convicted last year of strangling of four women and a 12-year-old girl in California in the 1970s. He has been sentenced to death.
He represented himself in court.