Very brief observations based on what is known so far:
1. @FoxSE14 - Hopefully local PE's are staying cautious and don't want to speculate. Although I did hear an FIU professor answer a few (not so great) questions of a local reporter.
2. There was one level of underground parking - this is actually not uncommon in this area - land is way too valuable to waste any, esp. when above ground gives you ocean view and there are height restrictions of the oceanside properties.
3. My guess would be that the columns holding the ground floor (the lobby/pool deck level) did not coincide 100% with the columns above.
4. Collapse looked, as others have pointed out, in the center of the building. (which ironically appears to be slightly shorter than the oceanside end)
5. As others have stated above: could be a 'simple' as a column being taken down in the parking, maybe the overloading of materials happened at the lobby/pool deck area rather than at the roof? I've heard random statements about a possible crane aiding with the ongoing roof work, but have not seen any sign of one or that being verified. It would be sad to find out the failure of ONE column would cause this, so maybe a transfer beam or punching shear failure would make more sense? Although with little redundancy if the floors above don't match the basement columns then this def could be a weak point.
It's hard to imagine a tragedy like this happening with no warning signs. Expecting the typical "stacking of mistakes" result.
God help the people still trapped and guide the responders to find them ASAP.
To whoever asked above why there is no recovery - there is! Miami Dade PD tweeted out a video showing them working through the flooded basement - this is no easy task to try to find Survivors and not compromise the debris pile
You can find the pictometry historical aerial views for free on the Miami Dade Property Appraiser site
-- sorry for long post, this has def hit way to close to home