” That doesn’t document how many shots were fired, nor who fired the shots.”
It documents who probably killed the gangsters.
Ballistics data is required to determine the caliber of weapon, and in this case, since the firearms were all rounded up and the police should not have ditched any, individual bullets should be able to be matched with the arms that fired them, provided the bullets are not too fragmented or distorted.
Then we will know who shot who.