Transcript for Fatal Fire Blast Classified as a Criminal Act
And we begin tonight with that deadly disaster, the explosion here in the U.S. That took the lives of 15 and destroyed dozens of homes. Tonight, authorities have now revealed it was, in fact, a criminal act. It began with a fire at a fertilizer plant in west Texas. And the massive explosion that followed, registering as strong as a magnitude 2.1 earthquake. So many lives lost on that night. Hundreds, in fact, were injured. But this evening, three years and 400 interviews later, what authorities have just revealed, as they now issue a major reward for help. ABC's Phillip Mena is in Texas. Reporter: We remember that father in the car with his daughter -- You okay? Yeah, I can't hear. Reporter: The explosion. The fear. Please, get out of here. Oh, my god. Reporter: The blast, the smoke seen from all over town. Families sheltering one another. Cowering behind cars. Roofs collapsed. The top floor of this apartment complex torn off. Oh, my god. People's houses are on fire. Reporter: Homes, neighborhoods on fire. Rescue teams racing in to help. Oh, my god. Reporter: 15 killed. Hundreds injured. And tonight, federal and state investigators say the fire that triggered the deadly explosion at a fertilizer plant in west Texas was intentionally set. The fire has been ruled as incendiary. This means this fire was a criminal act. Reporter: Authorities telling us, the hunt is on tonight for the perpetrator or person tray torps that took the lives or so many. We want the community to know that we haven't forgotten about those 12 first responders and the three other individuals living their lives. So, we owe it to them to go where this investigation leads us. Reporter: Lee years later, the town is still recovering. The community, the school here, coming back to life. And driving through neighborhoods today, we saw street after street rebuilt. Vy Talbot, happy to be home. You moved back? Yes, yeah. And Phillip Mena with us from west Texas. And you can see there behind you, Phillip, no sign of that plant that once stood right there. Any leads tonight after those 400 interviews? Reporter: Well, that's right, David. This empty lot behind me is all that is left from the blast. Authorities telling me tonight, they are following leads, but so far, no arrests, and no suspects. And tonight, a $52,000 reward is being offered.
This transcript has been automatically generated and may not be 100% accurate.