A notorious serial killer who admitted to murdering 13 people in the early 1970s has died in prison, the California Department of Corrections and Rehabilitation announced Friday.

Herbert Mullin, 75, died of natural causes Thursday evening. He had been housed at the California Health Care Facility and was serving two concurrent life terms for murder, the department said.

Mullin confessed to killing 13 people, both men and women, between Oct. 13, 1972, and Feb. 13, 1973, in the Santa Cruz area. Ten of his victims were shot to death. The other three were beaten and stabbed.

Mullin, who was diagnosed with schizophrenia, claimed the killings prevented earthquakes.