LHO had plenty of motive from simply being a Communist or Marxist and yes, it can not be proven beyond certainty, I believe Marina thought he shot at the extreme right-wing politician Scott Walker, there was some Marine shot out in the boonies where LHO was stationed in the Philippines, Oswald had a bad discipline record going back to his school days.
Marina’s testimony has been all over the lot as time passed, likely because of the FBI intimidation and threats of deportation. Her account of the Walker killing has internal contradictions which make it of little use.
Let’s pretend that she was speaking truthfully that Oswald told her he had “buried” the rifle after taking the shot. Of course, this tale impacts the ability of the rifle to make the shots at JFK. Now not only is the rifle taken hundreds of miles without a case between N.O and Dallas, but it has to have been cleaned after being dug up. (Of course, Oswald may not have dug it up) Then it has be be properly sighted as well. And it never was.
Another complicating factor for the theory is his alleged inability to hit a stationary target at a shorter distance than the world class shooting from the TBD.
Since JFK and Walker were deadly enemies and represented opposite ends of the political spectrum, it is unlikely that he would have shot both. In fact, it is ludicrous. JFK had relieved Walker of the US Army European Command after he passed out literature to the troops which was racist.
Oswald was part of it, that’s why he was silenced by Ruby. Conspiracies often include one killer who gets killed