Photo: AP

Federal officials announced on Wednesday that the 2013 fertilizer plant explosion in West, Texas, that left 15 people dead and 160 others wounded was caused by a “criminal act.” Twelve of those killed in the explosion were first responders.

Officials from the Houston Field Division of the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and the Texas State Fire Marshal’s Office said they came to the conclusion that the fire at the West Fertilizer Company plant was incendiary in the past several months.

The investigation “ruled out all accidental and natural causes,” ATF Special Agent Robert Elder said, but a motive has not yet been determined. “I think it’s too early to speculate on murder charges,” he added.

No arrests have yet been made. ATF is offering a reward up to $50,000 for any information that leads to an arrest.

Earlier this year, the United State Chemical Safety Board issued a report identifying at least 19 plants in Texas alone that are, like the facility in West, dangerously close to surrounding nursing homes, schools, and housing.

“It’s possible for another type of incident like this to happen,” agency Chairwoman Vanessa Allen Sutherland said at the time.