Diaz was born in 1938 and worked as a nurse on coronary care and intensive care units in Riverside County, California, moving between hospitals.
In March and April 1981 patients on wards where he worked died unexpectedly. Post-mortem examination found high concentrations of lidocaine, a drug used to control cardiac arrhythmia and dangerous in excess. He was arrested on November 24, 1981.
He was convicted of twelve murders and sentenced to death on April 11, 1984. He maintained his innocence for the rest of his life and died in prison on August 9, 2010.
The case has not gone unchallenged. Lidocaine concentrations measured after death are affected by post-mortem redistribution, in which the drug moves from tissue into blood and produces readings far above what was present in life, and the extent of that effect was not well understood in 1981. Defence and later commentators have argued that some of the twelve were critically ill patients who died of their conditions, and that the toxicology was over-read. The prosecution case also relied on the pattern of his shifts.
The entry records the conviction and records that objection. This is not a case where the convictions have been quashed or where any court has accepted the argument. It is one where the physical evidence rests on a measurement whose reliability has been disputed by people qualified to dispute it, and a reader should know that.