1) injected by mistake, concentrated potassium kills within seconds ; 2) the true incidence of potassium-related fatalities and incidents is unknown ; 3) fatal intravenous injection of potassium produces no specific anatomical changes and subtle, if any, findings at autopsy ; 4) it is used for capital punishment by lethal injection in various countries ; and 5) healthcare worker serial killers benefit from the fact that potassium is not identifiable in post-mortem examinations and that investigations to find the murderer are complex and of uncertain outcome.
https://pubmed.ncbi.nlm.nih.gov/32988194/