The fire that killed six people in a 35-story government office building n Chicago may have been started by malfunctioning light fixtures, investigators said Sunday.

An electrical engineer was hired to test the fixtures, wires and switches in the 12th floor storage room where the fire began Friday. The results may not be available for up to two weeks, said Tom Ahern, spokesman for the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.

Officials have said they do not believe the fire was arson.