Prince: 911 Caller Silent on Prescription Drug Run

The man who brought a synthetic opiate to the place where Prince was found dead won't talk about the investigation that focuses in part on him.

Andrew Kornfeld was at his dad's rehab facility Thursday when a photog asked about his decision to take the pills across state lines. We're told Andrew, who does not have a medical license, is under the microscope ... to determine if he's violated a law prohibiting the unlicensed practice of medicine.