This video of the 911 calls establishes a good timeline. By numerous accounts the garage roof/pool deck cratered first, a very good photo of the columns which punched through the deck can clearly be seen at 16:08 and starting at 15:04 one can clearly see where the rebar ripped out of the pool deck.
So...what exactly brought this building down if not a catastrophic structural failure caused by substandard rebar not to spec(?)/poor maintenance/a lack of competent monitoring of the structure/40 years of exposure to marine environment/sea water intruding into the parking garage to the degree that cars would be seen floating on some occasions.