This same thing happened to me 20 yrs or so ago. I left my wallet on the roof. I backtracked my drive and actually witnessed someone picking it up out of the street. I pulled over, they saw me and ran.

When I caught up with them, it turned out to be 2 teens who I don’t think had made up their mind what to do with the wallet when they saw me, so they panicked and ran. They jumped in a bush and threw the wallet out to me.

The lesson I learned from all this was never EVER set anything on the roof – and I haven’t since that day. If I must set something down (very very rarely), I set it on the hood directly in front of the steering wheel so that when I start the car, I will see what I’ve forgotten.