We Have A Ghost!!!

Last night I heard a crash that sounded like it came from downstairs around 11:45pm. I went to investigate but I could not see or hear anything out of the ordinary, so I went back to bed. But to our surprise, when Summer woke up this morning her room looked like the pictures below. The top of her desk was cleaned off, the lamp broken, the drawers pulled out and stood on end, and the contents were scattered about. What I heard was not any thing like what this should have sounded like. We can not explain any of it. Do you have any ideas on what could have caused this????