A cat broke into my house once too. It stayed in my room for 2 days before I noticed it. (Tells you how clean my room is, and how well used most of it is). I heard growling now and then, but I assumed it was outside my window, and didn't really do anything about it. One day I was going to bed though, and I heard a growl coming from underneath my bed. Now this I could hear perfectly well. I looked under, and there was this huge grey tomcat underneath my bed.
I tried to catch it, but it ran away through a hole in the wall (tells you how good of condition my room was in). The next day I found it there again, and I was determined to get rid of it once and for all. I snuck up on it ninja-style, and grabbed it by the back of the neck. It turned around and scratched the sh!t out of my arm, but I didn't let go. I instead let go of my grip on the back of its neck and instead starting choking the little prick. As the cat struggled for air, I threw it into a nearby box, and sealed it tight. I was intending to take it out back and finish the job, but as I was taking the box out the back door, it got out. I threw a few rocks at it, but it was gone before I could hit it.
That was one horrible little bastard of a cat.