SAN FRANCISCO (KRON) – One of four men convicted in a string of racially motivated killings around San Francisco in the mid-1970s was found dead in his San Quentin prison cell, according to The California Department of Corrections and Rehabilitation.

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.

Simon, 69, and three other black men — Larry Green, Manuel Moore and Jessie Lee Cooks — were convicted in a crime spree that took the lives of 14 victims and left seven white people injured. The four men, dubbed “Death Angels,” were sentenced to life with the possibility of parole

Simon was convicted in San Francisco County of two counts of first-degree murder, conspiracy to commit first-degree murder and assault with a deadly weapon.

Green, 63, is incarcerated at California State Prison-Solano (Vacaville); Moore, 70, is at Ironwood State Prison (Blythe); and Cooks, 70, is at Richard J. Donovan Correctional Facility (San Diego).

The murderous spree spanned six months, from October 1973 to April 1974, that gripped San Francisco. A San Francisco Police Department task force named the case “Zebra” after the radio band “Z” that was assigned to the case.