chapter 9-grim defeat

So after the halloween feast all the Gryfindors come back to the common room and the fat lady won't let them in...thats because the fat lady isn't there.  Peeves tells Dumbledore that Sirius Black is in the castle and the fat lady wouldn't let him in.  I can't believe filch doesn't know ALL the secret passages to get in and out of Hogwarts!