Investigators: Deadly Texas Plant Explosion Caused By Intentional Fire

A massive explosion at a Texas fertilizer plant more than three years ago was caused by an intentionally set fire, law enforcement officials announced Wednesday.

The fire and subsequent blast at the West Fertilizer Plant in West, Texas, killed 15 people, injured 300 and destroyed more than 500 homes on the evening of April 17, 2013.

The explosion prompted efforts by the Obama administration to overhaul safety regulations at the nation's chemical plants. The Occupational Safety and Health Administration also cited West Fertilizer for 24 safety violations, primarily over its storage of dangerous chemicals.

The Bureau of Alcohol, Tobacco, Firearms and Explosives, however, said that the fire that caused the explosion was “incendiary.” The agency said that it reached that conclusion after more than 400 interviews, reviews of evidence and footage at the scene and "extensive scientific testing."

"All viable accidental and natural fire scenarios were hypothesized, tested and eliminated," ATF officials said in a statement.

The bureau offered a $50,000 reward for information leading to the individual or individuals responsible for setting the fire.