Transcript for Sutherland Springs, Texas: Site of worst mass shooting in state history
souther land springs. The scene of unspeakable horror. Worshippers gunned down. It comes just 35 days after las Vegas. And if you look behind me tonight, you can see the massive presence. Federal authorities, the FBI, local authorities all here on the scene. This is the back side of the church. The front, tonight, they have cordoned off. This evening, the FBI truck stands in front of the first Baptist church where, of course, 26 lives were lost in a hail of bullets. The youngest, just a year and a half hold. About half of the victims were children. The pastor and his wife here, losing their own 14-year-old daughter. The shooter speeding away, good samaritans chasing him, ending in this field. It's believed the gunman shot himself. This is now the deadliest attack on a church in U.S. History. In fact, three of the deadliest mass shootings in this country, Orlando, Las Vegas and now here in Texas, all happening in just the last year and a half. Tonight, you will hear from the heroes, the man who took on the suspect in that parking lot. You'll also hear my interview with the driver who chased the suspect until his end. But we begin here with ABC's Matt Gutman, also here in Texas. Reporter: Tonight, squads of FBI agents combing the scene, as the pin dot-sized town of Southerland springs, Texas, shuddering from the loss in the deadliest mass shooting in Texas history. One thing everybody wants to know is, why did this happen? Reporter: Shortly after 11:00 A.M. Sunday morning, Devin Kelley, armed with a military-style rifle and two handguns, parked at this gas station and crossed the street to the first Baptist church. At 11:20 A.M., death barged into the church service. Devin Kelley murdering his way to front of the shoebox-sized church, seen here in video of past services with those tightly packed pews, and then, shooting his way back out. It was dozens of rounds. Reporter: Which means he must have had time to reload. Oh, yeah. Reporter: Almost no one was spared. All available personnel. Reporter: Police were on their way, but neighbors were already there. A local resident grabbed his rifle and engaged that suspect. Reporter: That citizen, Steven Willeford, hitting Kelley. Willeford then got more help from another citizen, Johnnie Langendorf. He said, chase him, so, that's what I did. I just chased him. Reporter: Jolting down a country road at over 90 miles an hour, during which, police say, the shooter called his father. The suspect used his cell phone to notify his father that he had been shot and didn't think he was going to make it. Reporter: He then lost control, crashed into a ditch where, police believe, he shot himself. Do we have helicopters in route? Three ems on scene correct? Reporter: He left behind a slaughterhouse. You can see first responders working on the wounded, and under that yellow tarp -- Dead body right there. Reporter: Neighbor David Casillas was there minutes later, weeping as he filmed. I seen family members coming out of the church with blood on their arms, you know what I mean, on their clothes, and they couldn't even talk, you know what I mean? They couldn't say nothing. Reporter: The victims raging from 8 months to 77 years old. When you see babies, young children, I mean, that's what -- that gets to you. Reporter: Police say up to 14 children in all, including pastor frank Pomeroy's 14-year-old daughter, Annabelle. We lost more than belle yesterday. And one thing that gives me a sliver of encouragement is the fact that belle was surrounded yesterday by her church family, that she loved fiercely. Reporter: Among them, members of a now decimated church youth group. Five of them are gone. Yeah. It's heartbreaking. That church is my family. And there's so many that are gone. It hurts so much. Matt Gutman with us live here tonight in Texas. And Matt, with 26 people killed here, that's really a substantial portion of this entire town. Reporter: That's right, David. That's the equivalent of 10% of the entire town's population, killed or wounded in that church behind me. And tonight, I spoke to a pastor who said that before they can even begin grieving, first, they have to bury the dead, and because there are several families facing multiple funerals, the community is coming together to help them pay for it.
This transcript has been automatically generated and may not be 100% accurate.