doctors charged with murder

A recent, bizarre murder case in Minnesota involved a physician (a poison expert) accused of poisoning his wife with a toxic gout drug called colchicine. The fact that she didn’t have gout, and that he had taken out a $500,000 life insurance policy, won’t help Dr. Connor Bowman‘s defense much. And a little lesson on the risks of using toxic drugs therapeutically.
More and more doctors are being prosecuted for murder, for inappropriately prescribing opioids to patients, resulting in death. How is it determined when a physician's actions have gone beyond malpractice?