Mitchell spent seven years in the military before leaving to pursue a civilian career.
News helicopter footage showed dozens of firefighters scouring the debris, with a group appearing to use a saw to cut through the wreckage.
The collapse happened in an area where construction had been occurring. (WABC)
The collapse happened in an area where construction had been occurring. (WABC)
Aerial videos showed firefighters digging at least one person out of the rubble. (WABC)