A former staff member who was arrested at a hospital in Kashiwa City, Chiba Prefecture for murdering an inpatient by mixing excrement into an inpatient's IV drip is suspected to have mixed it in through the ``plug'' that was used to inject drugs and other substances attached to the IV drip extension tube, according to interviews with the hospital and investigators. Police are investigating the possibility that the former employee chose a method that allowed him to mix things up in a short amount of time. In response to the investigation, he has denied the charges.