Transcript for Inside the Texas church shooting suspect's troubled past
Part of me hopes they're wrong and it's not her. Maybe she's just in the hospital. I want my daughter back. The last few days feel like a dream that Charlene would give anything to wake up from. She dropped her 16-year-old daughter off at church parting the way they always do. I told her I love you. I'll see you later. That's what we always said every time she left. She would never leave without kissing me goodbye. Giving me millions of kisses because wasn't okay to go to bed without kisses. That was just Haley. She was very loving. And she was always there. She couldn't have known it was the last time she'd see her constant companion. I wish my alarm hadn't gone off. Or I had woke up late so she wouldn't have been there that day. With survivors and loved ones crushed. The investigation grinds on. This is a massive crime scene. The warning signs about the man who methodically unloaded hundreds of bullets in a shoe box Texas church he had visited just days before. Now a portrait of a monster emerge emerging. While in the air force, he was convicted of assaulting his ex-wife and fracturing his infant son's skull. He carried out death threats against his superiors and said to smuggle weapons on to the base where he was stationed. He seems to be somebody who was angry. He had a past history of violent behavior. These are all characteristics we've seen in mass casualty attackers. This documented history should have he pr convenient him from purchasing the, it should have preventing him from purchasing the womens. The air force didn't notify the FBI of his conviction which would have precluded him from legally buyer a firearm. So when he went in to buy a gun, there was no record of his conviction in the air force. There was nothing in our database that precluded him from buying a firearm. The air force issuing a statement saying it has launched a review of how the service handled the criminal records of former airman Devin P. Kelley. We're going to take responsibility and find out what happened and fix it. Even if the air force had passed those records along, Kelley may have been able to acquire weapons through other means. There are informal ways or illegal ways. He can steal it or buy it off the black market in some way to acquire weapons. The reality is there are several million weapons in this country and a lot of assault weapons. If you're really determined to find them, you'll find them. The sporting goods store saying, both sales were approved by the national instant criminal back ground check system. Many of the survivors and their families would bear the emotional and physical scars. Like David brown's mother. The shooter was shooting everybody he could see. I guess everybody trying to run. And then after nobody was moving, just laying on the floor, he walked up and down all the aisles shooting everybody as they laid on the floor. How did she survive? Did she play dead? Pretty much. She just lay on the ground. And so many never made it out of the church. Including eight members of the Holcomb family, including three generations, including a pregnant mother and a 1-year-old. The whole family was beautiful inside and out. They were always there to help you. The debate over gun control once again coming to a head. President trump in South Korea. You've talked about wanting to put extreme vetting on people trying to come into the united States. I wonder if you could consider extreme vetting for people trying to buy a gun. If did you what you're suggesting, there would have been no difference three days ago. And you might not have had that very brave person who happened to have a gun or a rifle in his truck go out and shoot him, and hit him, and neutralize him. I can only say this. If he didn't have a gun, instead of having 26 dead, you would have had hundreds more dead. So that's the way I feel about it. But president trump's nominee for assistant sect of defense made this statement today. I would like to, and I may get in trouble with other members of the committee, to say how insane it is that the united States of America, a civilian can go out and buy a fully, a semi-automatic assault rifle like an ar-15 which is apparently the weapon that was used. This is not just an issue of gun control. This is an issue of being better able to identify people living in our communities, who are exhibiting the behaviors consistent with somebody preparing to carry out an attack like this. One key to identifying potential killers, past incidents of DMV like the ones in Kelley's criminal record. Devin Kelley a long history of being a dangerous person. We know that he abused animals. We know that he fractures the skull of his infant stepson. We know he tried on strangle his wife which is a huge indicator for someone who may commit a mass shooting. One study found 54% of mass shootings were tied to domestic or family violence. Investigators believe this killing spree was rooted in a domestic dispute. They say Kelley was hunting for his mother-in-law. These women are the canary in the coal mine for mass shootings. Samantha even highlighted this connection earlier this month. Mass shooters come in all male shapes and all male sizes but most rehearse for it the same way. This is OMAR Mateen's ex-wife who told ABC news he regularly beat her. You've got it. The common thread is domestic violence. It is incredibly important that we understand the implications of domestic violence. That we are ensuring they're prohibited from buying guns. Also that they have to relinquish the gun that's they already have. Local law enforcement in Sutherland springs, the FBI and the ATF have been able to unearth a great deal about the killer's motives and the time line of the day. But there's one resource they have not been able to tap. The phone of the suspect is turned over to us at this point in time. We are unable to get into that phone. Predictably most mass shooters, particularly his age, communicate electronically. To see what's on his phone may give you a window into what he was doing moments before the shooting. What is painfully clear here tonight at a vigil at the high school, it won't heal the hurt that has touched almost every one here. Or feel the absence left by so many lives senselessly taken during a Sunday service. So they lean on one another in song and faith to guide them through the darkest chapter this town has ever seen. For "Nightline." In Sutherland springs, Texas.
This transcript has been automatically generated and may not be 100% accurate.