New Haven mayor's office spokeswoman Jessica Mayorga says four people were trapped when the beam fell Monday morning.
Yale-New Haven Hospital spokesman Mark D'Antonio tells The Hartford Courant that one of the victims later died at the hospital.
Two remain at Yale-New Haven Hospital, one in critical condition and the other in serious condition.
A third person is being treated at the Hospital of Saint Raphael for injuries considered not life-threatening.
The names of the victims' haven't been released.
The federal Occupational Safety and Health Administration and New Haven officials are investigating.