Investigators have virtually ruled out arson as the cause of a blaze that gutted four floors of California's tallest building, and officials said the fire's single fatality and several close calls were the result of human error, not a malfunction of the elevators.

City and federal arson investigators were to hold a news conference Tuesday on their on-site probe of the May 4 fire that gutted four floors and damaged a fifth in the 62-story First Interstate Bank building.Although details of the investigation by the city's 12-member arson team and a 24-person unit from the federal Bureau of Alcohol, Tobacco and Firearms were not immediately available, fire and bank officials said the investigation virtually ruled out arson as the cause.

Other than discounting arson, however, authorities late Monday were only able to officially list the cause as "undetermined origin," said city fire Capt. Ralph Ramirez.