The worst nightclub fire in Thailand killed 67 people and wounded 103 two years ago.
Senior prosecutor Ruecha Krairuek said 40 relatives of the victims acted as co-complainants, and all seven defendants pleaded not guilty before the testimonies of 50 state witnesses began and were completed on August 21.
Among the many charges, the heaviest facing all the seven defendants is manslaughter, which carries a maximum 10-year prison term and/or fine of Bt20,000, he said.