Apartment Guru: Building Manager Lets Himself In, Watches TV

Dear Apartment Guru,

I think my building manager comes into my apartment when I'm not at home. He doesn't do much, but my theory is that he watches my TV and eats my cereal and other food that he thinks I won't notice.

I started suspecting when my downstairs neighbor was home sick one day and heard someone in my apartment. She called upstairs to ask if I wanted to hang out since we were "both" at home. She asked me later why I hadn't answered my phone. Then I started noticing little things, like the TV remote being moved and the level of milk in the container getting lower.

Mind you, I have no proof. There is another neighbor who swears she found the building manager at her door one day with his key in the lock. He told her that he was "chasing a rat" in the building. I don't want to falsely accuse him. How can I find out if he's letting himself in, and what can I do about it?

--A Girl Who Lives Alone