I'm big into true crime. One rapist/killer that beats all the previous mentioned ones is called The East Area Rapist/Original Night Stalker.
In California, beginning June 18, 1976 through 1979, he raped 40+ women, then moved to southern California in 1979 and began murdering couples in their homes through 1986.
Please read about him here. He's never been caught and they do have his DNA! He just had his 40th anniversary.