Homicide detectives are investigating the fatal fall yesterday of a construction worker at Wood Street and Fourth Avenue, Downtown.

A news release issued by city police this afternoon said it appears Brian Obermeier, 33, of Etna, fell 20 stories from the roof of the Commonwealth Building, adjacent to the former Union National Bank, which is being renovated.

He was pronounced dead at the scene at 10:46 a.m., the Allegheny County medical examiner said.

An investigator from the federal Occupational Safety and Health Administration was at the scene.