I know this might sound strange, but I had the same thing happen to me... 19 years ago. I took my ball python into the art room my senior year to do some live studies of it. 3 days later, the lid is off and my snake is loose in the highschool. I was just a stupid kid at the time. Had I known then what I know now, none of it would have ever happened. I suspected that someone stole her, but could never prove it. 5 months later she magically showed back up on the floor of the art room. To this day I don't know if she escaped or was stolen then returned.