I read a detailed report that pointed out the visible scarring from where the steel reinforcement was ripped out of the concrete. That is visible in the above photo. The consensus seems to be a three step collapse. The trigger point is the lower foundation near the pool wall and the basement garage. Once that failed it collapsed the center section of the building, the twisting and weight of the rubble pulled the supporting columns of the next section out of line and they failed. That lead to the final pancake collapse of the right side of the building.
It looks like a cascade failure. The bulk of the building was probably sound but the center failure damaged the next section and so on. The million dollar question will be why the center section foundation failed.