Officer Baker wore motorcycle boots, which would have made quite a racket on the stairs.
So much so that Garner, if she really was in the back room that early, could have thought it was Adams and Styles descending. The noise then stops for awhile (Baker confronting assassin Oswald) and then resumes, getting louder until Garner sees the two men run through the fourth floor. This round of noise on the staircase she correctly attributes to Truly and Baker.
Meanwhile Adams and Styles are over at the passenger elevator; they cross the fourth floor while Garner is busy looking out the windows or has gone back to her office.
You're a funny man...
Garner told Barry Ernest that the girls ran out of the office, through the back door, and she followed them seconds later. When she got to the stairs the girls were gone. What happened, Jerry? Did they just disappear in a puff of smoke?
Meanwhile Adams and Styles are over at the passenger elevator; they cross the fourth floor while Garner is busy looking out the windows or has gone back to her office. Nice bit of speculation. Too bad it doesn't work and it contradicts what Garner actually said. Styles was photographed in front of the main entrance of the TSBD at around 12:36 and went back into the building just before it was locked down. This could never have happened if the girls had left the 4th floor later than Adams said all along. So, how do you explain that? Can't wait to read your response...