A fire that caused an explosion which killed 15 people at a fertiliser plant, near the town of Waco in 2013, has been thought to have started intentionally, Texas authorities have said. Hundreds were also injured in the gigantic blast at West Fertiliser Company, 17 April 2013 and now, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) has posted a $50,000 (£34,000) reward for any information leading to an arrest, although no arrests have been made so far.

The cause of the blast, at 7.51pm local time, was a fire reported 20 minutes earlier which caused ammonium nitrate to ignite. Among the dead were 12 fire fighters and the blast left a crater that measured 90 feet (30m) wide and 12 feet (4m) deep, destroying 500 homes and schools in the process and with debris reportedly found two and a half miles (4km) away from the site of the explosion.

Authorities said if the blast had happened earlier, hundreds more people could have been killed. The financial costs were also enormous with an estimated $230m (£159m) in insurance-related losses and $100m £69m) in damage.

Before the explosion, there had been concerns about safety at the plant, with fertiliser and combustible materials stored in areas with poor ventilation. One theory investigators had been working on was that a golf cart stored at the facility had short circuited, but a $2m (£1.4m) inquiry has now ruled that out and said the case of the fire was incendiary.

"We have eliminated all reasonable accidental and natural causes. This means this fire was a criminal act," ATF Special Agent in Charge, Rob Elder, said at a news conference.

The widow of one of the firefighters killed said she hoped those responsible were caught soon. "I pray to God that they get caught and get the death penalty," said Kelly Pustejovsky, widow of Joey Pustejovsky. "No life deserves to be lost due to someone's stupidity, criminal mind set."