I might guess some "tidying up" was required on some material. Chain of evidence stuff that was found lacking first time around.
This is a Hoover memo dated 24th November (4.00pm) and declassified in 2017:
https://images.dallasobserver.com/media/pdf/docid-32263509.pdfThe pertinent paragraph reads:
"Chief of Police Curry I understand cannot control Capt. Fritz of the Homicide Squad, who is giving much information to the press. Since we now think it involves the Criminal Code on a conspiracy charge under section 241, we want them to shut up.
Furthermore, I have ordered the evidence be secured by the Police Department. We sent most of the evidence back to them. We still have the bullets that were fired and will keep them."There seems to be quite a lot of friction between the FBI and the DPD. Hoover, himself, ordered the return of the evidence to have it "secured by the Police Department". I don't know what this means and it sounds off. The very next sentence after this paragraph relates to Hoover wanting to "convince the public that Oswald is the real assassin".
Hoover is not impressed with the work of the DPD and believes it's the FBI who are doing all the important work:
"They did not really have a case against Oswald until we gave them our information. We traced the weapon, we identified the handwriting, we identified the fingerprints on the brown bag. We were able to identify the bullets as coming from that gun. All the Dallas Police had was three witnesses..."
The FBI did a lot of work on the 23rd but still had lots more to do. With this in mind, why would Hoover return all the evidence to the DPD when he is so critical of them?