Whether some other person fired the deadly shot, or brought a 2nd gun with the motivation or intent to use it. Other than Tyler. Even if they don't identify the other shooter, was there another gun present where the shooter considered using it on Charlie? If Tyler didn't do it, then obviously there is another. Or he had direct physical help moving the gun, before or after. Opening a door. Destroying evidence at the scene.

They did already destroy evidence. Negligently or on purpose. But was this coordinated?