Lock the door when you leave

I live in a gated community comprised of about 10 buildings, each one three stories tall, and interconnected by walkways. When I got home last night I found someone working on the front door of my building. About an hour later I left for the casino. As I got to the front gate I realized that I had forgotten to take my earphones with me, and since I enjoy listening to music as I playPoker, I went back to get them. I parked the car and went to the front door and it was locked. I asked my neighbor, who was getting out of his car, which he always parks in such a way so as to take up two spaces, if he had a key. He didn't and neither did the guard at the front gate. So I just walked around to the side of the building and entered there. Understand, they put a lock on the front door and the two side entrances have no doors!!!!