A 26-year-old man walked into a church in the small town of Sutherland Springs, Texas Sunday morning and killed 26 people, authorities said.

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

20 other churchgoers were injured in the shooting spree. Six victims are stable or have been released from the hospital, four are in serious condition and 10 victims remain in critical condition, the Texas Department of Public Safety said Monday morning in a press briefing.

The suspect was identified as Devin Kelley, who lives in a suburb of San Antonio a couple counties over from the First Baptist Church where he killed over two dozen people, law enforcement said at a press conference.

9NEWS learned Sunday evening that Kelley also lived in Colorado Springs in the last few years.

In a press conference Monday morning, the ATF said two of the four guns Kelley is alleged to have used in the massacre were bought in Colorado.

The other two were purchased in Texas.

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Voter registration records show Kelley was originally registered to vote in Comal County, Texas in 2009 - when he would have turned 18. He lived in Comal County before the shooting.

But in 2014, he registered to vote in El Paso County under a Colorado Springs address. In 2009 and 2014, he registered as an unaffiliated voter.

The FBI said Monday Kelley purchased the four guns over a four-year period from 2014 to 2017.

MORE INFO | Sutherland Springs church shooting: What we know now

The Pentagon put out a brief statement saying that he was, at one point, an airman in the Air Force. NBC News confirmed Kelley received a bad conduct discharge from the Air Force.

He served in Logistics Readiness at Holloman Air Force Base in New Mexico from 2010 until his discharge in 2014.

NBC News reports he was court-martialed in 2012 for two counts of Article 128 UCMJ, assault on his spouse and on their child. He was placed on confinement for 12 months and given a reduction to grade E-1.

The ATF Special Agent in Charge, Fred Malinowski, said Monday that typically a dishonorable discharge would prohibit a person from purchasing a firearm.

On Monday, the regional director of the Texas Department of Public Safety, Freeman Martin, detailed perhaps a part of the suspect's motives. Martin said Kelley had 'expressed anger' towards his mother-in-law, who was a member of the church in Sutherland Springs.

Martin said there was a 'domestic issue' within the family, and that the mother-in-law had received threatening text messages from Kelley.

Kelley entered the church during Sunday service dressed in all black, wearing a ballistic vest and carrying a Ruger AR assault-type rifle, according to the Texas Department of Public Safety.

He wore a black mask with a white 'skull face' during the shooting, according to the Texas Dept. of Public Safety.

As he left the church, a local resident spotted him and grabbed his or her own weapon and exchanged fire. Authorities said Kelley then dropped his gun and fled in his vehicle, with the local resident in pursuit.

Police would find him dead in his car a short while later.

Kelley's cause of death has not yet been determined, but a spokesperson from the Texas Dept. of Public Safety indicated evidence may show the suspect died from a self-inflicted gunshot wound.

9NEWS is naming the suspect in this shooting in case anyone who knew him can provide more information to investigators about what potentially led to the attack.

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