A black-clad gunman opened fire Sunday at a rural church outside San Antonio, killing at least 26 — including several children — and wounding at least 10, law enforcement officials said.

The killer, pursued by a good Samaritan with a gun, was found fatally shot a short time later in a neighboring Texas county, said a law enforcement official who is not authorized to comment publicly.

Authorities did not immediately identify a motive for the attack at First Baptist Church of Sutherland Springs, and they did not officially identify the gunman. But two law enforcement officials who were not authorized to comment publicly identified the gunman as Devin Kelley, 26, of nearby Comal County, Texas.

Kelley served briefly in the Air Force but was court-martialed in 2012, a military spokeswoman said.

Speaking to reporters late Sunday, Texas Gov. Greg Abbott said, "There are no words to describe the pure evil that we witnessed in Sutherland Springs today."

Abbott said officials were cautiously releasing information on the shooting, including the names of victims, who ranged in age from 5 to 72 years old.

Officials said 23 of the 26 victims were shot inside the church.

“There’s a lot of information," Abbott said. "We want to piece the puzzle together.”

Freeman Martin of the Texas Department of Public Safety said the shooter, who was dressed in black and was wearing a ballistic vest, was spotted at about 11:20 a.m. at a Valero gas station across from the church. Witnesses said he drove across the street, got out of his vehicle "and began firing at the church" with a Ruger assault-type rifle.

He moved to the other side and continued firing, then entered the church, Martin said, where he "continued to fire."

As the suspect left the church, Martin said, a bystander retrieved a rifle and began firing at the shooter, who dropped his Ruger and drove away.

"Our local citizen pursued the suspect at that time," Martin said.

As law enforcement responded, the suspect drove off a roadway at the Wilson County/Guadalupe County line, Martin said. He was found "deceased in his vehicle,” he said, but officials were not immediately certain if the fatal wound came from a self-inflicted gunshot or from the person pursuing him.

In a late Sunday news conference around the corner from the church, Wilson County Sheriff Joe Tackitt said as far as he knows the suspect had no ties to the town or knew anyone in the church, but that information was still being investigated.

“We don’t know why he was even here,” Tackitt said.

When asked if anyone has been able to describe to him the scene in the church, Tackitt replied, “All I can say is it was terrible.”

“It’s unbelievable to see children, men, women laying there,” he said. “Defenseless people. It’s just something you don’t want to see.”

Describing the layout of the church, the sheriff said he doesn’t think people could have escaped the attacker.

“You’ve got your pews on either side when you’re walking down the aisle and he just walked down the center aisle, turned around and was, from my understanding, shooting on his way back out," he said. "There was no way anyone could have escaped.”

Tackitt said he knew quite a few of the people who were in the church, later describing the community as one where “pretty much everyone knows everyone.” He said recently the church hosted a fall festival.

“A week later this happens,” he said.

He confirmed a family had been killed, though he didn’t confirm number of people in the family, describing it as a “a pretty high number.” Tackitt said he’s known the family “forever.”

Frank Pomeroy, who is pastor at the church, told ABC News he was out of town when the rampage took place, but that his daughter was killed. Annabelle, 14, "was one very beautiful, special child,” Pomeroy said.

Paul Buford, pastor of nearby River Oaks Church, said his service was underway when first responders in his congregation were called to the scene. He said some members of the community had "confirmed information" about family members and friends. Buford declined to provide any details.

"We are pulling together as a community," Buford said. "We are holding up as best we can."

President Trump, addressing the shooting before speaking to U.S. and Japanese business leaders at a meeting in Tokyo, said the federal government will give "full support" to Texas as it deals with the aftermath of the "horrific shooting" at the church. While these are "dark times," Trump said, Americans will do "what we do best: We pull together."

Trump ordered that the U.S. flag be flown at half-staff at the White House and elsewhere through Thursday.

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Police, ambulances and helicopters swarmed to the small church 35 miles east of San Antonio.

The Bureau of Alcohol, Tobacco, Firearms and Explosives said agents from its San Antonio office were responding to the shooting. The FBI also was on the scene.

Texas Attorney General Ken Paxton noted on CNN that Sunday's shooting took place eight years to the day after the 2009 shooting rampage at Fort Hood, which unfolded about 150 miles north of Sutherland Springs. In that shooting, Maj. Nidal Hasan killed 13 and wounded 32 in the deadliest domestic military attack in U.S. history.

Paxton said he wondered if there was a connection between the two shootings. "It’s just strange to me that it happened on the same day and in the same state," he said.

Kelley was previously in the Air Force and served in logistics at Holloman AIr Force Base in southern New Mexico from 2010 until his discharge, according to Ann Stefanek, an Air Force spokeswoman.

Kelley was court-martialed in 2012 for assaulting his spouse and their child. He received a bad conduct discharge, was confined for 12 months and busted to the grade of E-1. He was discharged in 2014.

Authorities on Sunday were examining the timing of the shooter’s acquisition of the firearms used in the assault Sunday, and whether he obtained them after he received the bad conduct discharge, a law enforcement official said.

Among those prohibited from possessing firearms, according to the Bureau of Alcohol Tobacco Firearms and Explosives, are those who have been discharged from the military “under dishonorable conditions,” said the official, who is not authorized to comment publicly on the matter.

Carrie Matula, who works at a nearby gas station near, told MSNBC she heard what sounded like semiautomatic gunfire coming from the modest, white clapboard church with a red door.

"This is something that happens in a big city," she said. "I would never have thought this would have taken place here. It's just too tight a community. It doesn’t make sense."

Elsewhere on Sunday, officials suspended a 20-year-old victory tradition at Texas Motor Speedway: the celebratory firing of a pair of pistols into the air.

Track president Eddie Gossage told USA TODAY Sports that the decision was made out of respect for the church shooting victims. "In light of what happened, it was the respectful thing to do,” Gossage said.

At a prayer vigil held across the street from the church on Sunday evening, people sang and prayed, candles in hand.

Debbie Jones, 55, said she was still trying to find out if a friend survived the shooting. "We’re just devastated," she said. "We’re just waiting."

Contributing: Kevin Johnson, David Jackson, Tom Vanden Brook, A.J. Perez and John Moritz, USA TODAY, and Eleanor Dearman, Corpus Christi Caller-Times.