In order to investigate the cause(s) of the collapse, I would need to know the live load of the meeting room and what is allowed in the meeting room (activities, amount of people, equipment, etc.). I would contact the D.O.B. to obtain original floor plans, specifications and inspections to find out if they were up to date and are up to code. I would need to know the conditions of the building and if there were any errors with the original construction.
I would proportion responsibility to the structural engineer being that they are responsible for structural integrity and failure as well as the building owner/manager whoever is in charge of facilitating programs/activities within this building and meeting room. They should be aware of the occupancy load.