I found an un-cashed money order at a property I just purchased..

[Joshua Parrish]

I recently bought a Tri-plex. It's got a supply room that's separate from the living units. The previous owner cut a hole in the door and made a drop box for the tenants to leave their rent in so they didn't have to mail it. I was there today doing some work and I found an envelope with an $800 money order made out to the previous owner. It had fallen out of the box and was stuck behind some other things where it was out of sight. My instincts tell me that when I purchased the property this became mine, similar to if I had found a safe or cash hidden the walls, etc., since a money order is essentially as good as cash. Am I right to assume this? And if so, how do I get the money into my account with another person's name on the payee line? Can I just go into the bank and deposit it? Can I cross the name out and put my name there. I want to stay on the right side of the law here so any advice would be appreciated. The property is in California.