Federal officials investigating the fertilizer plant explosion in West, Texas, have called the fire “a criminal act.” The announcement came during a Wednesday afternoon press conference by the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) not far from the explosion scene.

ATF Special Agent in Charge Rob Elder told reporters his team conducted over 400 interviews and performed a systematic investigation to come to the determination the fire was set intentionally, WFAA reported. The massive explosion that left fifteen people dead, 160 injured and at least 500 homes destroyed occurred about 20 minutes after the fire began.

“We have come to this conclusion through over 400 interviews, a systematic fire scene examination, considering witness observations, viewing both witness photographs and video, as well as extensive scientific testing,” Elder told the reporters. The testing was conducted at the ATF’s laboratory in Maryland.

At this time, the ATF stated that no arrests have been made in the case. Elder stated they had “many leads” as a result of their interviews and investigation.

The video below captures the intensity of the explosion at the 1:25 mark.

Shortly after the explosion, Breitbart Texas Managing Director Brandon Darby traveled to West to cover the tragedy and help with a Tea Party led relief effort to assist the victims of the explosion, Breitbart News reported. Darby had extensive experience with relief efforts in post-Katrina New Orleans and was then running Citizen Patriot Response, a group that mobilizes Tea Party and other liberty-minded groups to help communities in need. Darby began sorting through the fog of disaster and reporting the facts to the public-at-large shorty after last night’s tragic accident and continued reporting from the scene for several days.

The explosion in 2013 occurred at the West Fertilizer Company on April 17, 2013. Since that time, state and federal officials have been investigating the explosion. Officials said they have ruled out “all reasonable, accidental, and natural causes,” The Washington Post reported Wednesday.

The ATF reportedly spent over $2 million in the investigation. The agency is offering a $50,000 reward for information leading to the arrest of the person or people responsible for starting the fire.

Elder noted that 12 of the 15 people killed in the explosion were first responders. “These individuals were people serving their community in a volunteer capacity,” Elder told the gathered reporters. “They are true community servants. They lost their life serving their community and they deserve the best that we can give them.”

Bob Price serves as associate editor and senior political news contributor for Breitbart Texas and is a member of the original Breitbart Texas team. Follow him on Twitter @BobPriceBBTX.