Read the latest on the Texas shooting with Monday’s updates.

SUTHERLAND SPRINGS, Tex. — A gunman clad in all black, with a ballistic vest strapped to his chest and a military-style rifle in his hands, opened fire on parishioners at a Sunday service at a small Baptist church in rural Texas, killing at least 26 people and turning this tiny town east of San Antonio into the scene of the country’s newest mass horror.

The gunman was identified by the Texas Department of Public Safety as Devin Patrick Kelley, 26. Mr. Kelley, who lived in New Braunfels, Tex., died shortly after the attack.

He had served in the Air Force at a base in New Mexico but was court-martialed in 2012 on charges of assaulting his wife and child. He was sentenced to 12 months’ confinement and received a “bad conduct” discharge in 2014, according to Ann Stefanek, the chief of Air Force media operations.

The motive for the attack was unclear on Sunday, but the grisly nature of it could not have been clearer: Families gathered in pews, clutching Bibles and praying to the Lord, were murdered in cold blood on the spot.