20) Again, "could have" doesn't mean "did". If Oswald made such a trip in the required 75-90 second timeframe, he somehow managed to do it without being seen or heard by Victoria Adams and Sandra Styles who were in the same stairwell at the time, or by Dorothy Garner who heard Adams and Styles go down before Truly and Baker came up, or by any of the other 9 people who were on floors 4 and 5.
_You must be claiming that all those mentioned were actually listening for people on the stairs.