The cause of last month's fire that gutted a lighting store in downtown Wilmington remains a mystery for city fire investigators.

The cause of the fire at Gross Lighting Center on Aug. 22 has officially been labeled "open/undetermined" by the Wilmington Fire Marshal's office.  

Deputy Fire Chief William McKim says they've "investigated all leads which provided no conclusive evidence as to how the fire started."

The stubborn fire sent smoke billowing through downtown Wilmington last month and took firefighters hours to get under control.  The building at the corner W. 4th St and Orange St. was unoccupied when the fire started.  

It had been condemned by city inspectors in June 2012 after multiple violations of city building codes were discovered.  Those violations included improperly maintained electrical facilities, loose and damaged asbestos, a weakened floor, and unsafe structures and equipment.