Officials: Fire That Caused West Plant Explosion Was Intentionally Set

_{Editor's note: This story has been updated with comment from U.S. Sen. John Cornyn.}

Three years after a West, Texas, fertilizer plant explosion killed 15 people, including 12 firefighters and first responders, state and federal officials said Wednesday that someone set that fire, committing a criminal act.

The explosion on April 17, 2013, originated from the Adair Grain and West Fertilizer Company. The explosion damaged or destroyed buildings within a quarter-mile radius of the site. Witnesses reported feeling or hearing the blast from as far away as Arlington, 65 miles northwest of the Central Texas town.

Until Wednesday, the cause of the fire setting off the explosion was not clear. The explosion occurred when flames reached a tank of ammonium nitrate, a common fertilizer stored at the facility. Officials from the Bureau of Alcohol, Tobacco, Firearms and Explosives and the Texas state fire marshal's office said that after continuing to investigate and interviewing more than 400 people, they have ruled out accidental or natural reasons for the deadly blast, which also injured more than 200 people. 

"We don't know what the intent is because we haven't talked to the person or persons involved," ATF Special Agent in Charge Robert Elder said during a news conference in West. Elder said he would not get into specifics about the incident or law enforcement's thinking, including the type of charges they might pursue.

The bureau is offering a $50,000 reward for information.

During a conference call with reporters on Wednesday, U.S. Sen. John Cornyn praised the resiliency of West's residents and said Wednesday's announcement was a tough blow.

"It’s one thing to think that this might have been just an accident. It’s another to know that it could well be the result of an intentional criminal act," Cornyn said.

Julián Aguilar contributed to this report.