During the conversation, Hoover hots that FBI had yet to complete fingerprint analysis or ballistic analysis of CE399 or the bullet fragments found on SS100x's floor. The latter of these were what would tie the rifle to the assassination, and (as Hoover noted) the FBI had already tied the rifle to Oswald. That connection made the case much stronger.
Except there were no fingerprints on the rifle to connect it to anything. At least not in the first 24 hours after the murder, when the FBI lab in Washington examined the weapon and did not even find a trace of a possibly lifted print.
And ballistic analysis of the bullet now in evidence as CE399 was equally useless, as there is (1) no way to establish that CE399 was ever in Parkland Hospital or (2) fired by the MC rifle on 11/22/63.
The same goes for the bullet fragments that allegedly were found in the Presidential limo at the Secret Service garage, before Frazier and his men got there to examine the car. Frazier was given bullet fragments and told they came from the car. They apparently were collected by two men who didn't have a clue what they were doing and took no pictures of the items in situ and basically just tampered with evidence.
And finally, the only way Oswald is tied to the MC rifle is by the flawed opinion of an FBI expert who claimed that Oswald wrote the order note for Kleins' in Chicago which, in the bigger scheme of things, proves absolutely nothing even if it was true.
Amateur hour all over the place.... and that's what you rely on?