There’s the possibility that Oswald ( or other shooter ) could have used the East elevator if he had an accomplice who operated it, to take Oswald past the 4th floor unseen by Dorothy Garner and Oswald could have exited the elevator on the 2nd floor landing as early as 55 secs post shots.
The accomplice then operated the East elevator returning it to the 5th floor by 70-75 secs post shots where it would be then seen by Truly looking up the shaft.
That’s about the only reasonable alternative LN scenario imo, unless it can be determined that Mrs Garner waited at least 70 secs post shots before she came out which would be enough time for Oswald to have used the staircase and be starting down from 6th floor about 45 secs post shots and at a 10sec per floor descent , Oswald have gone down part of the 4th floor staircase and not be in LOS of Garner when she exited the 4th floor office door at 70 sec post shots.
I’ve got the earliest probable time for the SW 6th floor window shooter using the MC rifle found on 6th floor , to start down the staircase not earlier tan approx 45 secs post shots because of the added time required for wiping prints off the rifle while doubletiming across the 180 ft of floor (requires 25 secs of time ) and for the act of slowly withdrawing the rifle after it took several secs for Bob Jackson to spot the rifle, a few more secs to exclaim “there’s a rifle in the window” and a few more seconds fir Macolm Couch to look up and find the window thaf Jackson was pointing at.
The shooter also had to get up from the box he was sitting on and turn around with the rifle and then had squeeze thru a narrow opening ( per Tom Aleyas observation of the original gap that existed in the wall of boxes before it was widened)