First, please hire an experienced lawyer immediately to preserve the evidence!
From experience with malfunctioning doors, I would highly recommend that you also retain someone who has installed, serviced and repaired the type of door (and preferably the very type of door) involved. Also hire a very competent mechanical engineer, but the installer/repairer's insight and practical knowledge at the site inspection with an engineer is invaluable in nailing down the probable cause of the door's failure. Get the manufacturer's installation guide, service manual, owner's manual, etc.. You may find that scheduled maintenance was never done. In addition to the surveillance video, demand the post-incident repair records and all prior service, installation and repair records be preserved. When you find out who (if anyone) serviced the door, request their independent records. You may find quotes for work that never got authorized. Conversely, you may find recent repairs or maintenance service was improperly done. If documents and other valuable evidence are not preserved with a proper spoliation letter, you may not be able to prove your case.