Cause of Fire That Led to West, Texas Plant Explosion Still Undetermined

One month later

Investigators say the fire at the West Fertilizer company plant caused two powerful explosions last month, killing 15 people, 12 of them firefighters.

State Fire Marshal Chris Connealy says, "I don't recall a tragedy of recent times in Texas, and certainly one of the worst in American history with first responders."

After a nearly one month long investigation involving 29 state and federal agencies and more than 100 people, the state fire marshal and ATF say they have ruled the cause of the fire undetermined.