Who do I talk to about a nurse that took a patients medication instead of giving it to the patient?

The nurse was supposed to give medication to the patient. Nurse was observed going into the patient's bathroom for several minutes, exited the bathroom and put the syringe in a sharp's container. When confronted, the nurse refused a urine test and while being escorted from the Hospital, looked over at the patient's room, and stated Yea, I did it. Nurse then contacted the nursing supervisor several times the next day stating that he had hid medication in several other rooms. This nurse had been fired from previous jobs for the same thing.