Okay I know that you are probably scared to do this but you need to speak with your parents as soon as you can.   The police have only "circumstantial" evidence but do not get me wrong: it could be enough if you were trespassing and the only ones found in the school.  However, the fact that you were approached in the school with out the laptops and that the door was unopened gives some reasonable doubt that you may not have been the only people in the school that day.  Get an attorney asap.  Good luck.