What makes this class of offense so difficult to detect and prosecute is that perpetrators target victims who are severely ill, even terminally ill, who cannot speak for themselves. Such patients are vulnerable to death from natural causes and to health-care professionals who can intentionally inject lethal doses of therapeutic substances, or even essentially toxic substances, in the presence of eyewitnesses. Often there is no autopsy. End-stage Alzheimer's patients, cancer patients, comatose persons, or the elderly and ill thus become targets for murderers in the health-care professions. Even if such crimes can be detected, proving them requires extensive medical evidence and winning a battle of the experts, which may include a "Daubert" challenge to the admissibility of the evidence. In one of the cases described in this article, murders of two elderly nursing home patients were suspected because of the suspicious timing and circumstances of their deaths, as well as several admissions made to coworkers by the defendant. The case was driven by expert witnesses who clashed over the relative significance of extremely high postmortem morphine levels in a cancer-ridden nursing home patient. In another case, a serial murderer was detected due to a "spike" in the death rate at a county hospital after the defendant was hired. A supervisor's investigation was turned over to the State police, who began an exhaustive, 2 1/2-year investigation. The investigation included interviews with and testimony by medical experts and the execution of search warrants for the defendant's home. These cases indicate that often the most difficult element of proof pertains to the cause of death. The prosecution must prove that the victim's death was not a natural death and that the defendant's actions caused the death of the victim. The intent of the defendant's actions, even if proven to have caused the death, is another issue that determines degree of culpability. These evidence issues require qualified expert medical testimony as well as testimony by coworkers and others who have had relevant conversations and experiences with the defendant. In addition to detection and evidence issues, this article also discusses charging decisions, legal issues, jury considerations, and motive. 22 notes