You’re waiting outside the building that the unsub is very likely located, Reid went in a few minutes ago to investigate and asked you to wait outside. A few gunshots ring out and you immediately lift your gun and run inside, looking for him. As you run into the bathroom, you see Reid standing there in silence with a shocked look plastered on his pale face. Your eyes drift to where he’s staring and see the unsub’s body and Reid’s gun on the floor. He shot the unsub and is in absolute shock.