There is no firing pin mark on the empty Luger cartridge case, so it had never been fired.
The first photo on Judith's phone shows an indentation, when zoomed in the casing has none.
When the brick is thrown through the glass pane in the door at Judith Potts's house, the sound of breaking glass is heard while the camera is on Judith, who looks up when she hears the noise, then, in the next scene the brick is shown breaking through the glass pane - an action which had apparently already occurred.