The Texas fertilizer plant where an explosion injured more than 100 people and killed an unknown number of others was cited for failing to obtain or to qualify for a permit in 2006.
The Texas Commission on Environmental Quality investigated West Fertilizer on June 20, 2006, after receiving a complaint June 9 of a strong ammonia smell.
Agency records show that the person who lodged the complaint said the ammonia smell was "very bad last night" and lingered until after he or she went to bed.
Wednesday night's explosion leveled the plant and severely damaged other area buildings. Authorities say people were killed, but they don't know how many.
Authorities were still trying to evacuate area homes early Thursday morning.