There is no federal law requiring records being kept for sales between individuals. Gun dealers have been required to keep records of gun purchases since 1938. The fact Oswald decided to purchase a rifle via mail order rather than from a private seller is evidence of nothing. Trying to read Oswald's mind an any point in time is a futile effort.
We don't have to read his mind. A mere two days after completing his preparations for the attempt on Walker, and while living in the most gun-happy, gun-friendly state in America, he chose to buy a cheap rifle by mail from a dealer in Illinois using his own post office box and an alias when he could have easily bought a better rifle that would have been completely untraceable right there in Dallas. This is what he
did, regardless of
why. The law allows a judge or jury to draw reasonable inferences from the evidence. There is a clear disconnect that, together with other evidence, might lead to reasonable inferences that there was no such preparation, or Oswald didn't order the rifle, or Oswald had no intent to shoot at Walker.
This is likewise true with history. Historians are entitled to draw reasonable inferences, and sometimes their reasonable inferences are quite different. You seem to want to think that the LN narrative itself is a
fact, when it simply isn't. It's a plausible account of what occurred, but it isn't sacrosanct and it isn't without problem areas. I have highlighted some of the aspects that nag at me, not in an effort to read Oswald's mind but to try to make sense of what he did in the context of the LN narrative - or any other narrative that might more plausibly explain what he did.
Ditto with his choice to assemble his rifle and set up the sniper's nest on the 6th floor of the building where he was employed, having no way to control who might be on that floor and having little chance of escaping without being seen, captured or killed, when he could have exited the building with his "curtain rods" and set up in a location far less risky. Again, we are talking about what he
did, not
why. One reasonable inference might be "He didn't do that. He wasn't on the sixth floor." - which happens to be exactly what he claimed.
I'm not saying by any means that the only reasonable inferences favor some conspiracy theory. I'm simply saying that when we look at the
evidence of what Oswald
did, much of it seems somewhat problematical for the LN narrative.