OK, first of all, you'll need the episode in which Max's boss gets an electric shock in the head.
Secondly, you need to watch carefully when Max's boss fires his gun and Michael and Isabel.
Thirdly, Watch as a bit of the wall falls out leaving a big hole in the wall
After a while, when the NEW sheriff goes and tries to get into the room where they all are, he looks at the bullet hole.
Now it looks like a normal bullet hole, and the part that fell out is back in place.