PITTSBURGH -- Investigators said they're confident they know what happened, but they still can't say why a construction worker fell 20 stories to his death from the roof of a Pittsburgh building Tuesday morning.

ADVANCE VIDEO: Workers Arrive At The Scene

Funeral services were held Friday for Brian Obermeier, 33, of Etna, who fell 20 stories from a building at a construction site at the corner of Fourth Avenue and Wood Street in downtown Pittsburgh.

He was pronounced dead at the scene.

Police said Obermeier was part of a crew converting the former Union National Bank building into luxury condominiums. Police said he fell from the roof of the Commonwealth Trust building next door.

Workers were accessing the Union National building by going to the top of the Commonwealth Trust building.

Authorities said Obermeier was last seen getting off the elevator at the 20th floor and heading toward the stairs leading to the roof.

The Allegheny County medical examiner and the federal Occupational Safety and Health Administration are investigating why Obermeier fell.