Did you see this video of the collapse?
OMG! :*( I don’t think I can pray any harder for all the people involved with this!! :*(
Nothing much on the video other than it probably wasn’t C-4 or terrorists.
My WAG (and right now everyone who says what made it happen is guessing) is that there was a fatigue crack in a non-redundant tension member. It may have been covered up by a facia, bird crap, or soemthing else. Or, it may have been where it was difficult for the “snooper truck” to reach and the inspectors just eyeballed it from a distance. Or maybe someone just falsified the records, saying they looked but didn’t. In any case, the crack finally got large enough that it could not hold the load with rush-hour traffic and it broke. When it broke, the entire rest of the bridge came down.