We have a state politician trying to get this done here in Oklahoma. It has opposition from doctors. One was quoted on camera citing the doctor's pledge to stay out of executions. it appears somewhere in 1994 the AMA declared a doctor is prohibited from declaring an inmate dead, something about the focus of a doctor is on helping a patient live and not certifying a criminal's death upon execution.
made me wonder if non capital crime felons could donate an organ, or part in the case of a liver and earn parole.