Making things worse, the state will probably try to have a "state inquest," meaning whitewash.
I know that airports are federal jurisdiction now. One thing that illustrates that is that state "no mask required" mandates DID NOT APPLY in airports while the federal one was in place.
Those cops, be they Dallas or State, were out of their jurisdiction, though that doesn't mean that they cared. After all, if the police do it, it's not illegal in some places.
No matter who fired first, I think every one of the cops present can be tried for anything from accessory to murder IN A PLACE SUBJECT TO FEDERAL JURISDICTION, meaning that it's a federal case. I doubt that the Nuremberg defense will work, especially since I suspect that a lot of papers and logs are being "lost" with impressive speed.
For that matter, people who gave whatever orders were given could possibly be arrested as accessories.
Once again, I'm surprising myself by thinking Hoover isn't acting decisively enough. Getting federal search warrants from a "tame" judge shouldn't be too hard, and then seize every bit of documentation related to the case. If I understand things correctly, every state or city official on Air Force One could be in federal custody. Since there is possible evidence of treason or espionage, if he wanted to over reach, Hoover might even seek out a warrant to seize EVERYTHING related to the assassination. (Or would it be overreach? Once again, I'm shocking myself by saying that Hoover isn't acting aggressively enough.)
Worst (and super extreme) case is that the warrants are resisted, and more gunfire ensues. If that happens, it becomes a case of whe declares martial law first: The president or the acting governor of Texas.
The government of Texas is effectively paralyzed due to the governor being in surgery and recovery. Lieutenant Governor Preston Smith should be involved right away ; this is bigger than a city. Among other things, he should, IMVHO, be telling the cops to shut the heck up.
The amount of biological waste product that has become colocated with the rotary air impeller is sufficient to cover EVERYONE!
One possible source of evidence, if police radio recordings either weren't made, or "failed to record due to technical issues," would be people listening to police scanners, be they ordinary people or reporters. (I don't know how popular police scanners were then, but in the late 70's, they were quite popular. Hear a siren, turn on the scanner. In some households, including ours, it was usually on. You could tell instantly when something was major instead of routine.
The "technical issue" involved, of course, being a series of very strong magnets applied to the tapes in question.