Wilson County officials say more than 12 of the 26 victims killed in a South Texas church shooting over the weekend were children.

Devin Kelley, 26, opened fire during a Sunday morning service at First Baptist Church in Sutherland Springs, south of San Antonio.

Twenty-six people were killed and 20 others were injured. The gunman was found dead in Guadalupe County a short time later.

Wilson County Sheriff Joe Tackitt said Monday that he personally knew about a dozen of the victims and couldn't confirm if the shooting is domestic-related, though he did confirm that the shooter's in-laws sometimes attended the church.

The names of the victims haven't been officially released, but the church's pastor confirmed that his 14-year-old daughter, Annabelle Renee Pomeroy, was one of the victims.

The ages of the victims range from 5 to 72 years old, and Tackitt said Monday that the number of children killed could reach 20.

The Floresville Independent School District, where many of the victims likely attended school, released the following statement on Monday:

"We are devastated by the tragedy in Sutherland Springs. Our hearts are breaking for the families of the deceased and injured. These are our community members, friends, students and their families. While we continue to learn about the specifics of this horrific event, we want our FISD family to know that we are prepared to provide grief counseling services to our students and staff affected by this senseless act of violence. FISD counselors and counselors from San Antonio and surrounding areas will be available first thing Monday morning to provide support to our students, families and staff.

Because of the location of the incident, several bus routes will need to be adjusted. We will be contacting the riders in the affected locations. We ask for your patience as we navigate the road closures that are occurring. We understand that this is a difficult and concerning time for our community and want you to be assured that we will continue to be vigilant in our efforts to monitor our campuses.

Please keep all those affected by this evil crime in your thoughts and prayers."