By "bridge" you mean the triple underpass. I don't think the spot you've identified on the triple underpass is a plausible shooting location.
As if any place other than the sixth floor sniper's nest is viable, given the forensic evidence available.
However, I will point out that the first thing that DPD Chief Jesse Curry and Sheriff Bill Decker did after the shots rang out was to order their men to go to the area of the triple underpass and the railroad yard behind the grassy knoll to see what had happened, clearly indicating they believed shots had come from somewhere in that area.
Which indicates they had no special powers of audio perception and could be fooled as to where the gunshots originated from.
And of course we know from the photographic evidence that large numbers of people in the plaza, including some police officers, rushed toward the grassy knoll after the shots were fired. We also know that J. C. Price saw a man running away from the grassy knoll fence and into the railroad yard right after the shooting. A number of witnesses said they smelled the pungent odor of gun powder on or near the knoll right after the shooting. And, the Wiegman film shows a small cloud of smoke hanging in front of the trees on the knoll, which confirms the eyewitness accounts of seeing gun smoke emitted from a point just behind the fence on the knoll during the shooting.
All those people rushed to the GK and not one of them saw a gunman. Nor did Lee Bowers who was watching from an elevated position from behind the GK. You guys scoff at the SBT as requiring a magic bullet, then try and tell us there was a magic shooter who disappeared into thin air after firing the kill shot from behind the wooden fence.
As for the smell of gunpowder, the people who reported that were on Elm St. when they smelled it. Unless you want to argue the shooter fired from Elm St., that indicates the smell originated from a location some distance from Elm St. You would have us believe the gunpowder residue they smelled could travel to Elm St. from behind the wooden fence but not from the sniper's nest. A really illogical take on those reports.