Testing the gun requires firing the same kind of ammunition into a special test tank to retrieve the spent round, and then microscopically comparing it with the round retrieved from Abdul's body during an autopsy to match the striations left by the weapon's rifling. There was no time to do this and no time for Abdul's body to have been autopsied, so there was no way to know what weapon was used to kill him.
The microfiche document is marked Top Secret but has a Confidential stamp too. These were two different classifications and no document would be labelled with both.