Since the fastest probable time for a shooter from 6th floor SE window of the TSBD whom had to wipe prints off, after slowly withdrawing rifle, and squeezing out of cramped SN, cross 180ft to boxes and wedge rifle in a narrow gap, is probably at least 30 sec post shots..
and since the fastest probable descent time per floor going down is approx. 10sec/floor
then its going to take the shooter at least 53 secs post shots to be completely past the 4th floor landing and halfway down the 4th floor staircase to be out of LOS of anyone who was standing with LOS to the staircase earlier than 53 sec post shots.
The question is, if Dorothy Garner would have waited 53 sec after having seen Adams and Styles leave the office window and go out the door, before following them out herself. And how probable is it that Garner would remember a 53 sec delay as having followed "almost immediately" and "right behind" A&S?
This might be resolve more definitively if Mrs Garner could elaborate on exactly what she "heard" when she told Barry Ernest about having "heard them" on the staircase, as opposed to having actually seen A&S, as the original statement in the Belin memo described.
IF Garner heard voices, its not very probable to have emerged at 53 sec posts shots and then it takes another 10 sec to travel to the staircase west window, such that Garner would have heard voices at 63 sec post shots. V.Adams and Styles would on the 1st floor then, and very probably just exiting the rollup door right beside the west elevator. Could their voices at normal decibel range have carried up the open elevator shaft as far as the 4th floor?
IDK!? Its apparent that SHOUTING down the elevator shaft from 5th or 6th floor can be heard by people on the elevator going down the shaft as per Oswald haveing been heard.
But Truly shouted UP the elevator shaft at about 70 sec post shots, and no one seems to have heard that, including Jack Dougherty who was only 10 ft away from the shaft according to JD.
So IDK if it can be 100% ruled out as impossible that Garner could have heard the voices of V.Adams and Styles as they reached the ground floor at approx 60 sec post shots as they were going past the west elevator open shaft, which was open all the way to the 4th floor, since both elevators were fixed on the 5th floor at that time, via by Truly seeing them at 70 sec post shots.