At a Thursday afternoon news conference, State Fire Marshal Chris Connealy said that officials are ruling the cause of the fire that triggered the April 17 explosion of the West Fertilizer Plant “undetermined”.

Because multiple causes could not be confirmed or eliminated, investigators could offer no clear picture of what happened to trigger the two nearly simultaneous explosions that caused between 28 and 34 tons of ammonium nitrate to erupt with the force of 20,000 pounds of TNT. The possibility of arson is still on the table, but officials have presented no evidence that would support the theory at this time.

You can watch the news conference below.