In interviews with detectives after being arrested, the therapist confessed to having overdosed selected patients by injection with either pancuronium bromide (Pavulon) or succinylcholine chloride. He subsequently recanted his confession, claiming his admissions were the result of his suicidal depression. Subsequent police investigative efforts included the exhumations of 20 patients selected from a list of some 100 suspicious deaths of patients who had been accessible to the suspect. Exhumed tissue samples from lungs and kidneys were processed for pancuronium following a protocol developed for extracting, concentrating, and identifying the drug. Pancuronium was deemed detected and confirmed when the prescreen of tissue extracts by pyrolysis gas chromatography-mass spectrometry (GC-MS), followed by subsequent mHPLC-ESI-MS/MS, were both positive for pancuronium. The results of these experiments indicated that 6 of the 20 patients had detectable levels of pancuronium in their tissues. The ESI-MS/MS mass spectrum of pancuronium is very specific. The doubly charged molecular ion, m/z 286, generates a unique MS fragmentation pattern; however, to fully exclude false-positive data possibly generated by other compounds in the tissues and fluids, the medical records of all exhumed patients were further reviewed to determine whether the pancuronium-positive patients had been administered any other drugs with molecular weights or other characteristics that could potentially generate false-positive MS data. Based solely on these analytical results, the respiratory therapist was rearrested, followed by a plea-bargain arrangement. 2 tables and 8 references