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In an extraordinary turn for one of the ATF's most labored and expensive fire investigations ever, the agency said Wednesday that the deadly blaze that destroyed West Fertilizer Co. in West, TX, in 2013 was a criminal act, and it pleaded for the public's help to find who was responsible.

The news immediately opened old wounds in this small, agricultural town north of Waco, reignited rumors, frustrated residents trying to move on with their lives and threatened to complicate a mound of litigation against the plant and its suppliers, the Houston Chronicle reports.

Investigators for the Bureau of Alcohol, Tobacco, Firearms and Explosives spent more than $2 million, building life-size replicas of parts of the plant and interviewing more than 400 people, to reach the conclusion that the fire was set in the seed room, Elder told reporters. Victims' families were briefed hours earlier. The news conference was held at the Knights of Columbus Hall that served as an aid station in the blast's immediate aftermath.

The plant exploded 14 minutes after the first 911 call on April 17, 2013, killing 12 firefighters and three others, injuring more than 260 and causing an estimated $230 million in losses. The blast left a crater 93 feet wide and 12 feet deep.

The damage was inflicted across a 37-square-block area, destroying more than 500 homes, apartments and a nursing home. Had it happened earlier in the day, with school in session, hundreds more people, including children, would likely have been killed and injured.