Joseph Naso, 79, faces the possibility of being sentenced to death for killing Roxanne Roggasch, 18, in 1977; Carmen Colon, 22, in 1978; Pamela Parsons, 38, in 1993; and Tracy Tafoya, 31, in 1994. Authorities said the victims were raped, strangled and dumped along rural roads.
It took the jury less than a day to convict.
Naso, who represented himself during his two-month trial, is to be sentenced during a hearing before the same Marin County jury that is to start Sept. 4, the San Francisco Chronicle reported.
If given the death penalty and executed, Naso would be the oldest person ever put to death in California.
Authorities believe Naso may have killed others but he has not been charged in those cases.
Swim Week Miami Beach 2014 [PHOTOS]