The TSA is going to take all the bridge rubble and try to rebuild it somewhere, to see if they can determine what caused the failure.
A person commented on CNN (I think it was a structural engineer), that he can not imagine, HOW, two ends of the bridge came down at the same time.
There was some jackhammer work on one side of the river, that might have contributed to 'vibrations', but, an investigation was needed to determine if the jackhammer work was specifically around, or close to, critical connectors (? bridge talk) that may have caused/contributed a span failure.