We still don't have a witness that saw Oswald use the elevator or stairs. Excuse my Perry Mason approach to evidence.
BTW, did anyone listen to the radio show in the original posted link? It was an informative.
***When I was a young lad of about 10, I would race my Aunt's elevator by using the stairs. She was on the third floor. I could beat her going down, but up, the elevator beat me about half the time. This was a matter of 15 seconds, or less, for a 10-year-old to go three flights. For Oswald to go 4 flights down, would likely be no different. Also, going down, I was rarely out of breath or sweating. Going up? Different story.***
Would have been a little difficult, it was about 5-and-a-1/2 years before my time.
I'm just saying that time was not an issue, as, if he was the shooter, he could have easily traversed 4 flights in a matter of seconds. Lack of witnesses was not my point.