The suspect, whose identity authorities confirmed as Devin Patrick Kelley, sent threatening text messages to his mother-in-law, who sometimes attended the First Baptist Church in Sutherland Springs, Texas, where the shooting took place.

"We know that he expressed anger towards his mother-in-law, who attends this church," said Freeman Martin of the Texas Department of Public Safety in a press conference on Monday.

"There was a domestic situation going on within this family," Martin said.

Officials told reporters that none of Kelley's family members were in the church at the time of the shooting. Wilson County Sheriff Joe Tackitt Jr told CNN on Monday that Kelley's in-laws attended the church "from time to time", but were not there on Sunday.

At least 26 people were killed and 20 others injured after Kelley allegedly opened fire on the church during the Sunday morning service, police said. Ten people remain in critical condition.

Kelley was shot outside the church, police said, and was later found dead in his car after a police chase.

The results of an autopsy on Kelley's body are expected to be released soon.

Martin said, however, that "investigators found evidence at the scene that indicates the subject [Kelley] may have died from is a self-inflicted gunshot wound". Who is Devin Patrick Kelley?

Martin of the Texas Department of Public Safety confirmed that the suspect is Devin Patrick Kelley. Kelley was 26-years-old. He resided in New Braunfels, Texas, in the greater San Antonio area.

Kelley is believed to have opened fire with an assault rifle, which was recovered at the scene of the church. Kelley also had two handguns in his car, police said.

Kelley did not have a license to carry a gun, Martin said. He held an unarmed, private security license "similar to a security guard at a concert", Martin said.

Kelley had a clean record in the Texas and national crime databases, Martin said.

He was seen at a gas station near the church before the shooting took place.

He was dressed all in black and he wore a black mask with a white skull over his face.

Kelley was also wearing a bullet-proof vest with a protective plate on the front. The vest did not have a plate on the back.

However, Martin said "investigators found evidence at the scene that indicates the subject may have died from a self-inflicted gunshot wound".

Kelley had purchased four firearms since 2014. He brought one gun annually between 2014 and 2017. Two were purchased in Colorado and two others were purchased in Texas.

Kelley served in the US Air Force from January 5, 2010 to May 9, 2014, a spokesperson for the Air Force confirmed in an email to Al Jazeera.

He spent most of his time in the Air Force at Hollowman Air Force base in New Mexico.

What happened in Sutherland Springs, Texas?

The shooting took place at the First Baptist Church in Sutherland Springs, Texas, during the 11:00am (17:00 GMT) service.

The suspect is believed to have moved around freely inside the church. When the shooting began, a call went out to local police about an "active shooter" situation, Martin said.

Upon hearing what was going on, a resident who lives near the church heard and took his own assault rifle and "engaged the suspect", Martin said, adding that gunfire was exchanged at the church.

Kelley was shot outside the church, dropped his assault rifle, and fled to his vehicle.

As he was being pursued by police in his vehicle, Kelley texted his father "that he had been shot and didn't think he was going to make it", Martin said.

Police have recovered a video from inside the church, but did not give any details of what, if anything, it revealed.

The FBI is assisting local police and other officials with their investigation. The crime-scene investigation is expected to go on for several days. 

Who are the victims of the Texas church shooting?

At least 26 people were killed: Twenty-three people were killed inside the church, two were killed outside the church, and one died in hospital, Freeman Martin said.

The deceased victims range in age from 18 months to 77 years old.

Another 20 people were injured. Of those who were injured, ten remain in critical condition, four are in serious condition, six are stable, and four have been released from hospital, according to Martin. The 14-year-old daughter of the church's pastor was also killed, local media said. The pastor and his wife were not present at the time of the shooting.

News24