. . . and we know Oswald had reassembled his rifle prior to using it to kill JFK.
You don't "know" any such thing. As I have already proved to you, the ammo that hit JFK's behaved nothing like the ammo that Oswald allegedly, and the paraffin cast of Oswald's right check was tested with NAA and came back negative for any trace of gunshot reside, proving he did not fire a rifle on the day of the shooting (the FBI confirmed with a control test that the NAA was 100% accurate -- the paraffin cast of every single shooter in the control test tested positive for gunshot residue; in other words, NAA detected gunshot residue in the paraffin cast of every single shooter in the control test, an accuracy rate of 100%).
No wonder the FBI suppressed the results of the NAA testing of Oswald's right paraffin cast.
It is unnecessary to prove when he did it.
Of course! Yeah, who needs proof when you're emotionally committed to believing in Oswald's guilt?! This is right up there with your declarations that "I don't need a rational explanation" and "I don't need to be objective."
You've already proved you have no credible answer for the evidence that puts Oswald on the first and second floors of the TSBD shortly before, during, and within 40 seconds after the assassination. This is why Roy Truly did not see Oswald when Truly crossed the second-floor landing and headed up the stairs to the third floor no more than 85 seconds after the shooting, even though he was running 5-10 seconds ahead of Officer Baker. Oswald was already in the second-floor lunchroom when Baker saw him because he had just come there from the first floor to get a soda.