So, once you know that Oswald denied owning the rifle, then you study the alleged timeline of him ordering it and getting it, and you realize that it is filled with inconsistencies, incongruities, and deal-breakers. He really didn't own a rifle, and everything that Marina said about him and it was fabricated out of whole cloth- which is scary to think about but true And note that George DeMohrenschildt wisely refused to say that he ever laid eyes on the rifle. He was willing to go along, but he knew better than to say that. He knew that one could blew up, so he left himself an out.
And it's the same way with the Mexico City trip. You start with the fact that Oswald denied going there. Now, why would he do that if he really went there? He was being accused of killing the President of the United States and a police officer, so why would he lie about something as innocuous as going to Mexico City? And why would he think he could get away with such a lie if he knew that he was there and there were hotel records, embassy records, witness recollections, etc.?
And likewise, why would he lie about not posing for the Backyard photos if he really did? Wouldn't he have known that his wife was going to confirm that he did pose for them and she did take them? What would be the point of lying about it?
It's a huge problem that we have people who claim to be Oswald defenders, yet, they still treat him like trash, where they just assume that he repeatedly lied to police (which an innocent person accused of murder wouldn't do). And, they also assume that zany, wacky, weird, eccentric Oswald would rather sit in a room alone doing nothing rather than join others to watch a once-in-a-lifetime historic event involving the President of the United States. Of course, Oswald was outside watching the motorcade. Why wouldn't he be? Where else was he going to be? The problem with some Oswald defenders is that they are really Oswald accusers masquerading as Oswald defenders.