Here is Brennan in Z133 the first frame of Zapruder's film in his 2nd sequence. As can be seen Brennan is not looking up towards Oswald even though Oswald's shot-1 was at Z112 (shot) Z113 (slug hit) Z114 (sound hit) which was 19 frames earlier ie 1.1 sec earlier (based on 18.3 fps).
[edit 15nov2023][shot-1 was at Z102, hit at Z103, sound at Z104, which is 29 frames earlier, ie 1.7 sec earlier]
Brennan thought that it was a backfire or a firecracker. Brennan's workmate Millican also wearing a hard hat is on the extreme left in the frame, he said he heard 7 or 8 shots or something, Brennan heard only 2 shots (including the backfire).
Brennan in a frame from the Dorman film. Dorman was on the 4th floor 2 floors lower than Oswald.
Brennan in a frame from i think the Hughes film. Toni Glover & mum are on the pillar that Brennan hid behind later.