Do I stalk him?

I found out 3 years ago that I don't know who my biological father is. I confronted my mom (we don't talk anymore) and she told me who she thinks he is. They dated in high school in NY. My mom called his old home phone number and talked to his mom. She said he was "going through something right now." So now wouldn't be the best time to be confronted with this situation. But that was 3 years ago.

This man is super private, hard to find any info online, and I'm pretty sure he's paid to have it that way. I sent a letter to him when I found out about him, but never got a reply. I live in PA and I think he has relocated to AZ. I found someone with his name there and had my friend call his office and talk to him. He had a NY accent!

I'm going out to AZ for a conference. I want to know if this guy is my real dad. Do I try to call him? Do I show up at his house? Do I wait for him to leave work? Do I stalk him? Do I hire a PI to do it?