A window washer at the Smithsonian's National Museum of the American Indian has fallen at least 50 feet to his death.

D.C. Fire Department spokesman Alan Etter says rescuers were called to the museum on the National Mall about 10 a.m. Thursday. It's not clear whether the man's safety harness failed or whether it had been engaged properly when he started work.

Authorities have not been able to identify the man. Etter says he appeared to be in his early 30s and worked for a contractor hired by the Smithsonian.

The Occupational Safety and Health Administration is investigating.