The church member who killed a gunman who opened fire during a Sunday morning service in Texas has given details of the incident.

Jack Wilson, head of security at West Freeway Church of Christ in White Settlement, told local TV new station KTVT that he had "eyes" on the suspect as soon as he walked into church.

"After he shot [the two victims], he went and started towards the front of the sanctuary and that's when I was able to engage him, and I fired one round," he said.

The shot immediately killed the gunman, who has now been revealed as 43-year-old Keith Thomas Kinnunen.

Wilson, who’s an FBI veteran and firearms instructor, added that he had no choice to but kill Kinnunen.

“The events at West Freeway Church of Christ put me in a position that I would hope no one would have to be in, but evil exists and I had to take out an active shooter in church," he said in a statement on Facebook.

"I am very sad in the loss of two dear friends and brothers in Christ, but evil does exist in this world and I and other members are not going to allow evil to succeed.”

He added: “It is a close knit congregation. It is a close family type situation. I’m concerned and I’m upset for that. I don’t feel like I killed a human, I killed an evil.”

Texas Attorney General Ken Paxton commended Wilson for saving many lives.

"My understanding is, he was a reserve deputy and had significant training, had his own shooting range, had taught other people how to shoot, had taught many people in this church how to be prepared," he during a press conference.

"He's not just responsible for his actions, which ultimately saved the lives of maybe hundreds of people, but he's also responsible for training hundreds in that church."

According to the Texas Department of Public Safety, the two victims were also members of the church security tram have been identified as Anton Wallace, 64, of Fort Worth and Richard White, 67, of River Oaks.