SAN FRANCISCO — J.C.X. Simon—one of the so-called "Zebra Killers" convicted of multiple murders of white San Franciscans in the 1970s—has died, prison officials said Friday. Simon, 69, was pronounced dead at San Quentin prison at 11:59 p.m. Thursday after being found unresponsive in his cell, Department of Corrections and Rehabilitation officials said. The cause of death is unknown pending the results of an autopsy.