The truth usually comes out on such things due to public interest.
Not a lawyer, so I don't know about such evidence, but agree it should both be looked upon skeptically, but also examined and tested.
My guess on testing the ammo was to compare it to what was in the gun, fire a round through the gun to see who closely they matched and run any standard chemical tests to determine, if possible, manufacturer and lot number of the ammo in the pistol...given there was more than one live round in the gun.