The cause of the deadly explosions at a Texas fertilizer plant last month remains undetermined, state and federal officials said Thursday.
Robert Champion, the agent in charge of the Dallas office of the Bureau of Alcohol, Tobacco, Firearms and Explosives, said at a briefing that investigators hadn't been able to rule out the possibility that the two blasts at West Fertilizer Co. were caused by an intentionally set fire.
The briefing was delayed a half-hour so authorities could talk to the families of the victims, said state Fire Marshal Chris Connealy, who promised to "leave no stone unturned to make sure everything is done."
On Thursday investigators said they still don't know what caused the initial fire, but they have ruled out smoking, weather and spontaneous combustion. NBC's Brian Williams reports.
"This community has suffered a great tragedy," he said, adding that 30 different local, state and federal agencies were working "with one common goal: to understand what happened so we can give closure to these families."
The explosions in the town of West, near Waco -- which killed 15 people and injured hundreds of others on the night of April 17 -- devastated a 37-square-block area, creating a crater 93 feet wide and 10 feet deep, Champion said.
Twelve of the dead were firefighters and other first responders, and Champion paid special tribute to them.
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