Drug detection in decomposed cadavers confirms testimonial evidence in a case of serial homicides

•Four people died rapidly after an acute episode that needed EMT intervention.•Eyewitnesses stated unrecorded IV injections of a milky solution.•PMIs, type of burial and state of preservation were different for all the exhumed.•Propofol, diazepam, midazolam and morphine were the molecules to determinate.•Results supported the testimony of administration of the alleged drugs.