Kenneth Lancelot Silvera, an 82-year-old man, died at Community Hospital of the Valleys in Perris, California, during the early morning hours of April 14, 1981. He had been admitted to the hospital’s intensive-care unit after experiencing chest pain and heart palpitations. Physicians were considering a possible myocardial infarction, and he was also suffering from congestive heart failure with pulmonary edema, a buildup of fluid in the lungs.
His medical condition was serious, but what happened during the overnight hours would later become part of one of California’s most disturbing hospital murder prosecutions.
Registered nurse Robert Rubane Diaz was working in the intensive-care unit that night. At approximately 1:00 a.m., Diaz administered a 100-milligram injection of lidocaine to Silvera to treat a heart-rhythm problem. At about 1:26 a.m., additional lidocaine was administered through an intravenous drip. Roughly half an hour later, Diaz told another nurse that he was increasing the dosage. Within about ten minutes, Silvera suddenly began suffering violent seizures. Hospital personnel responded to the emergency and managed to stabilize him for a time.
The crisis was not over. At approximately 7:15 a.m., Silvera stopped breathing. Witnesses later gave somewhat different accounts of what occurred immediately beforehand. Some nurses remembered another episode of seizures, while others did not. One witness testified that an IV containing lidocaine prepared by Diaz had been given shortly before the episode, while another recalled no lidocaine being administered at that point, and a third said a lidocaine infusion had been used only briefly and was stopped before Silvera’s condition deteriorated. Resuscitation initially revived him, but only minutes later another medical emergency developed. At approximately 7:32 a.m., efforts to save Silvera failed and he died.
Silvera’s death did not remain an isolated hospital fatality. Community Hospital of the Valleys had been experiencing an alarming series of sudden deaths and violent seizures among patients during the period when Diaz was working night shifts in its intensive-care unit. Investigators eventually examined numerous deaths at hospitals where Diaz had worked. The prosecution’s theory was that patients were being deliberately given massive overdoses of lidocaine, a drug routinely used in much smaller amounts to control dangerous heart-rhythm disturbances. Evidence later presented in court included unusually concentrated lidocaine solutions discovered in hospital syringes, testimony that Diaz carried lidocaine and syringes in his pockets, and lidocaine and medical supplies recovered during a search of his residence.
Silvera’s case became particularly significant because prosecutors argued that his violent seizures were characteristic of severe lidocaine poisoning. A prosecution medical expert concluded that the first seizure episode was consistent with Silvera having received more than 1,000 milligrams of lidocaine. The same expert believed that another overdose of at least 500 milligrams was administered before the respiratory emergency at approximately 7:15 a.m., followed by at least another 500 milligrams before the final emergency that ended in his death. Toxicologists who examined Silvera’s tissue samples found concentrations they considered far greater than could be explained by ordinary therapeutic treatment. They estimated that he had received roughly 1,000 milligrams of lidocaine shortly before death, an amount considered potentially lethal. A prosecution pathologist ultimately attributed Silvera’s death to lidocaine poisoning associated with hypertensive heart failure.
Diaz’s defense disputed that interpretation. Defense experts argued that Silvera’s serious underlying heart and respiratory problems offered an alternative explanation for his deterioration. One physician testified that he could have died from respiratory arrest resulting from severe congestive heart failure and inadequate oxygenation, while another attributed the death primarily to hypoxia with several contributing factors. The defense also emphasized inconsistencies in witnesses’ memories of the seizures and pointed out that most of the nursing documentation did not record them. Nevertheless, the trial judge ultimately accepted the prosecution witnesses and experts as sufficiently credible and concluded that the evidence established that Silvera had been murdered through a lidocaine overdose. The California Supreme Court later ruled that there was substantial evidence supporting Diaz’s conviction for killing him.
The wider investigation took months. Authorities examined a large number of suspicious deaths in Riverside, San Bernardino and Los Angeles counties associated with facilities where Diaz had worked. On November 23, 1981, investigators arrested Diaz at his Apple Valley home. He was ultimately prosecuted for 12 murders—11 patients from Community Hospital of the Valleys in Perris and one patient from San Gorgonio Pass Memorial Hospital in Banning. California formally charged him with 12 counts of murder and sought the death penalty.
Diaz waived his right to a jury and was tried before Riverside County Superior Court Judge John Barnard. The lengthy trial began on October 31, 1983, and relied heavily on medical testimony, toxicology evidence, hospital records and circumstantial evidence connecting Diaz to the patients immediately before their sudden collapses. On March 29, 1984, Barnard found Diaz guilty of all 12 counts of first-degree murder and found multiple-murder special-circumstance allegations true. Silvera was one of the victims for whose murder Diaz was specifically convicted.
On April 11, 1984, Diaz was sentenced to death. His conviction and death judgment later went before the California Supreme Court, which affirmed the judgment while striking redundant special-circumstance findings. Diaz continued to maintain his innocence. He was never executed; after more than two decades on California’s death row, he died of natural causes on August 11, 2010. Kenneth Lancelot Silvera’s death therefore became not merely one of the mysterious fatalities that initially alarmed hospital personnel and investigators, but one of the murders that resulted in Diaz’s conviction as the perpetrator of a series of deliberate hospital poisonings.
