Sacramento police say they arrested suspect Joseph James DeAngelo, 72.
The suspect has been living in the Sacramento area and was identified after new efforts to solve the case, investigators say.
Police blame the so-called Golden State Killer for 12 murders, 45 rapes and 120 burglaries.
Mr DeAngelo was arrested on two counts of murder with special circumstances.
Police had been monitoring the suspect and used “discarded DNA” to match him to the crimes, according to Sacramento County Sheriff Scott Jones.