Having had 24 hours to look at the photos and video it seems almost certain that the bridge failed in the section in the image at #2464. More specifically I think it has to be that left kingpost.
While the investigators might find subtle differences from what has been suggested here I doubt that we are far off.
I think it happened right in that area, but I’m just not comfortable with a trigger failure being attributed a member under compression.
I’m probably prejudiced on this, because each member is engineered based on what type forces it is expected wot withstand, but my gut likes tension failures first, shear and torsion tied for second place, and compression failures last.
That said, the discoloration on the other side at that location tells me that something was going on in the bottom chord, or that something had gone on in the past at that location. Frankly, the transverse dark brown lines near the northern end of the western beam look like either joints or cracks. That’s not a great place for a joint, much less so for a crack, and I don’t see other joints in other members showing that color either.
We’re approaching the edge of granularity here, in what we can discern from the available imagery, but I’m reasonably confident we aren’t on the wrong end of the bridge. Feel free to ping me when more develops, whether that is later today or a year from now, and I’ll return the favor if I turn anything up. I’m very much interested in getting deeper into this, but recognize the likelihood we’ll have to wait a long time for definitive answers.