One of the four men convicted of participating in a string of racially motivated attacks in the mid-1970s that killed 14 people and injured seven in San Francisco was found dead in his cell.

The California Department of Corrections and Rehabilitation said Friday that the body of J.C.X. Simon was found in his one-man cell shortly before midnight Thursday. The cause of death is unknown, and an autopsy is planned.

The 69-year-old was convicted of two first-degree murder charges in 1976 and was serving a life sentence with the possibility of parole.

Simon and three other black men were convicted of participating in the six-month spree known as the "zebra murders" that resulted in 14 deaths and seven injuries of white people in San Francisco in 1973 and 1974. The three others are serving life sentences.