Suspicious guy sits outside my workplace for hours at a time, changes cars and seems to be taking notes?

Over the past few weeks a co-worker and I have noticed a man sitting in a black BMW outside our work place. He parks on the far side of our (small) lot, with the front end of his car facing away from our building. We are in a shared warehouse complex so there is more than one company here, including a chop-shop type business and a print shop.

He often sits for a couple of hours at a time and looks like he's writing a lot of stuff down. Well, today my co-worker noticed he was in a different car than he usually is, and mentioned she's seen him in an SUV as well. Another co-worker walked in on our conversation and after hearing the story, she said "I'll go ask what he's doing!" and proceeded to walk up to his car and chat with him through the window.

Apparently he was flustered and trying to hide his paperwork from her. She asked why he sat there so much and his story was that he works down the street and parks here to eat lunch. (We've never seen him eating like some of the people that stop in our lot, he just writes things down or sits there doing nothing.) She asked why he has multiple cars and he didn't have an answer. We saw her turn away from the car to head back into our building and he was pulling hastily out of the lot before she even got back inside.

At first I thought maybe he was a private investigator, but if he is, he's not very good at his job because we noticed him weeks ago.

I will be taking note of the license plate if we see him again but I'm not sure we will, seems like my colleague scared him pretty good.

Any guesses on who he might be or what he might be doing?