Inside the largest mass shooting in Texas history: ‘Anybody he heard– he’d go and shoot them.’

SUTHERLAND SPRINGS, Texas - Chilling details are coming out of Sunday's mass shooting at the First Baptist Church where police say lone gunman Devin Patrick Kelley opened fire killing 26 people.

Kelley entered the church dressed in all black, wearing body armor, a black mask and carrying an assault rifle. Among the 26 people killed were a dozen children and an 18-month-old toddler!

"Never in a million years would I expect anything like this," a local resident declared. "I could never imagine anything like this ever happening here."

The church's visiting pastor was among the dead-- as was the regular pastor's 14-year-old daughter.

"People were screaming, 'Somebody call the police! Somebody call the police!'" David Brown, a Houstonian whose mom-- Frida-- was shot four times in the leg, revealed after talking to his mother. "And she says she thinks he was shooting their phones."

"It's just a horrific sight," Wilson County Sheriff Joe Tackitt recalled. "I mean, you don't expect to walk into a church and see something like that."

"We are dealing with the largest mass shooting in our state's history," Governor Greg Abbott announced.

"To the wounded and the families of the victims, all of America is praying for you, supporting you and grieving alongside of you," President Trump conveyed from Japan.

Authorities say 20 worshipers were injured in the bloody massacre, including Frida Brown, who is now recovering in a hospital in Floresville.

"And then the gunman came in, and he walked up and down the aisle, shooting everybody if they laid on the ground," Frida's son, David, said. "He said nothing. He'd just-- anybody he heard he'd go and shoot them."

Police say a good Samaritan outside the church, armed with his own weapon, shot the suspect, but Kelley was still able to get into his vehicle and flee the scene.

Then another witness, Johnnie Langendorff, chased him.

"We hit about 95 going down 539 trying to catch this guy, until he eventually lost control on his own," Langendorff shared.

Police later found Kelley dead inside his vehicle in a ditch.

"However, investigators found evidence at the scene that indicates the subject may have died from a self-inflicted gunshot wound," Regional Director of Texas Dept. of Public Safety Freeman Martin told reporters.

Authorities believe a domestic dispute led Kelley to go berserk, but there were definitely some red flags leading up to the deadly assault.

Officials say he sent threatening text messages recently to his in-laws, who occasionally attended the church Kelley targeted.

In 2012, Kelley was dishonorably discharged from the air force over accusations of spousal abuse and child abuse.

Kelley lived in New Braunfels and had worked five and a half weeks at Schlitterbahn Waterpark last summer as a seasonal, unarmed night security guard, according to Schlitterbahn.

Schlitterbahn indicates all of their security guards must pass a criminal background check through the Texas Department of Public Safety, but they say Kelley's employment was terminated.

Still, no one seems to be able to answer what could make anyone commit such an unthinkable act?