Officials say the Texas gunman sent his mother-in-law threatening texts and killed himself

The man who authorities say carried out the deadliest shooting in Texas history died Sunday following a police chase.
There's no official cause of death yet, but investigators believe the shooter, identified as Devin Patrick Kelley, fatally shot himself.
At least 26 people died in the massacre at the First Baptist Church in Sutherland Springs.

Devin Patrick Kelley, the man identified as the gunman who fatally shot at least 26 people at First Baptist Church in rural Texas on Sunday, was found dead in his car after a brief police chase.

Though an official cause of death has not been released, investigators believe Kelley shot himself after the massacre of people attending Sunday-morning church services in Sutherland Springs, a small town near San Antonio.

Authorities have been trying to piece together the timeline of the shooting, which Gov. Greg Abbott called the deadliest in the state's history.

More details about the victims, Kelley's possible motive, and the massacre itself began emerging Monday.

Officials are investigating whether Kelley was motivated by a hostile "domestic situation" involving his mother-in-law, identified as Michelle Shields. They do not believe the massacre is related to terrorism.

During a press conference on Monday, Christopher Combs, a San Antonio-based FBI agent, said Shields had previously attended the First Baptist Church but was not present Sunday during the attack. Combs also said Kelley had sent Shields threatening text messages.

Kelley purchased four firearms — two in Colorado and two in Texas — from 2015 to 2017. Three of them, a rifle and two handguns, were found at the scene of Sunday's attack.

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What happened on Sunday

According to Freeman Martin, the regional director for the Texas Department of Public Safety, Kelley parked his car at a gas station across the street from the church at about 11:20 a.m.

Kelley then crossed the street, exited his car, and began shooting at the church from the outside with a Ruger military-style rifle, Martin said. He continued shooting as he moved to the right side of the church, eventually entering the building.

Once Kelley exited the church, Martin said, Kelley was "engaged" by a rifle-wielding resident who lives next-door to the church. At that point, Kelley dropped his weapon and sped away in his vehicle while the resident followed.

After a brief chase, deputies found Kelley dead in his car off the side of the road in neighboring Guadalupe County. Kelley was wearing black "tactical-type gear" and a bulletproof vest, Freeman said.

During the chase, Kelley reportedly texted his father that he had been shot and didn't think he was going to make it.

Wilson County Sheriff Joe Tackitt speculated Monday morning that Kelley shot himself.

"At this time we believe that he had a self-inflicted gunshot wound, after he wrecked out," he told CBS News.

Officials say the Texas gunman sent his mother-in-law threatening texts and killed himself

What happened on Sunday

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