5.56x45mm NATO casings and .223 Remington casings are visually identical save for the stamp on the base of the cartridge (thickness of the casing in the 5.56 is slightly thicker).
To summerize what you're saying, the young soldier who passed away in Borden on the rifle range did so by gunshots, and civilian .223 caliber casings were found on the scene, and not military issue 5.56mm casings?
Furthermore, a soldier was charged with some kind of weapon offences shortly after in which the ammo present was civilian .223 bullets, that were somehow related to the previous shooting death.
You think the soldier was murdered, or shot by accident/negligence, and the CFNIS didn't bother investigating the evidence connecting the shooting and the weapon charges.
You have no idea what the other soldier was charged with?