Local, state and federal law enforcement agencies are working together on the investigation of a fatal apartment fire Saturday morning.  One person was killed and another suffered critical injuries at the Executive Apartments in Beaver Dam.  Four other residents were taken to a hospital for treatment of fire-related injuries.  No names have been released yet.  The weekend’s fatal fire came just one month after a man was killed while apparently working with explosives in another Beaver Dam apartment.  Authorities are still trying to determine the cause of the latest fire.