Prince: 911 Caller Tight-lipped During Death Investigation

Andrew Kornfeld, the man who flew to Prince's home on a thwarted rescue mission that ended with his call to 911, made it clear to a photog Thursday ... he wasn't going to talk about the ongoing criminal investigation into the singer's death.

Andrew's dad, rehab specialist Dr. Howard Kornfeld, got the call from Prince's rep the day before the singer died, pleading with him to come to Minnesota to save Prince from a fatal OD. The doctor couldn't make it but sent his son, who was in the house when Prince was discovered in the elevator.

As we reported, Andrew is under investigation because when cops arrived they found pills -- a synthetic opiate used to treat Percocet addicts -- in his backpack. Andrew, who is not a doctor, is being investigated for the unauthorized practice of medicine.

The photog got Andrew at a nature preserve in Northern California.

We also got video Thursday of Dr. Kornfeld outside his rehab facility, Recovery Without Walls, in Marin County, CA. He was also mum.