By Jason Hanna, CNN

(CNN) -- A gunman killed at least 26 people and injured about 20 others at a Texas church Sunday morning in what Gov. Greg Abbott said was the largest mass shooting in state history.

How the attack unfolded

Around 11:30 a.m. local time, a man dressed in all black exited a vehicle and started firing a rifle outside First Baptist Church in Sutherland Springs, a Texas community of a few hundred people about 30 miles of San Antonio, said Freeman Martin, a regional director with the Texas Department of Public Safety.

The man then entered the church, where services were underway, and continued to fire, Martin said.

A cashier at a gas station across the street from the church told CNN she heard about 20 shots being fired in quick succession.

Eventually, as the gunman was leaving the church, a local resident armed himself with a rifle "and engaged" the shooter, Martin said. Martin didn't say where the resident got the rifle, nor did he provide details about the engagement.

The shooter dropped his gun -- a Ruger AR "assault-type rifle" -- and fled with the resident in pursuit, Martin said.

The shooter drove north into neighboring Guadeloupe County, authorities said. Just inside that county, law enforcement officers found him dead inside his vehicle with a gunshot wound, Martin said.

"At this time, we don't know if it was a self-inflicted gunshot wound or if he was shot by the local resident" who chased him, Martin said.

Casualties

Of the 26 who have died, 23 were found dead inside the church. Two bodies were found outside. One person died after being transported to a hospital, Martin said.

Among the dead is the 14-year-old daughter of the church's pastor, Frank Pomeroy, according to his wife, Sherri Pomeroy, the girl's mother. The couple were traveling out of state when the shooting occurred.

At least eight of those killed were members of one family, according to a family member and a community leader who both spoke to CNN.

One of the deceased was about 5 months pregnant, and three of her children were killed. The pregnant woman's brother-in-law -- her husband's brother -- and a young child were also killed, according to the community leader.

An additional 3 members of the same family were injured in the church shooting, according to the community leader. The family member tells CNN that one of them was shot in the head.

About 20 people were taken to hospitals with injuries ranging from minor to severe, Martin said. At least four hospitals received patients from the shooting.

Victims ranged in age from 5 to 72 years old, Martin said. It wasn't immediately clear if that included just those who died, or all who were shot.

Authorities didn't immediately release the names of the dead and injured.

A community vigil was Sunday night held across the street from scene.

The shooter and the investigation

The church attacker was Devin Patrick Kelley, 26, according to two law enforcement sources who have been briefed on the investigation.

Without naming Kelley, Martin described the shooter as a young white male who was dressed in all-black "tactical-type gear" and wearing a ballistic vest. Multiple weapons were inside the vehicle, he said.

Martin said Sunday evening that he couldn't announce any information about a motive in the shooting.

Kelley previously was a member of the US Air Force. He served in logistics readiness at Holloman Air Force Base in New Mexico starting in 2010, according to Air Force spokeswoman Ann Stefanek.

Kelley was charged in military court in 2012 on suspicion of assaulting his spouse and their child, Stefanek said. Kelley received a bad conduct discharge, confinement for 12 months, and was demoted to E-1, or airman basic, she said.

Kelley purchased the gun he used, a Ruger AR-556 rifle, in April 2016 from an Academy Sports + Outdoors store in San Antonio, a law enforcement official told CNN. He listed an address in Colorado Springs, Colorado, when he bought the rifle, the official said.

When Kelley filled out background-check paperwork at the store, he checked a box to indicate he didn't have any disqualifying criminal history, the official said.

There was no disqualifying information that showed up in Devin Kelley's background check as he was trying to buy the rifle, a law enforcement official told CNN.

The FBI responded to the scene of the shooting, according to Michelle Lee, spokeswoman for the FBI's San Antonio field office.

Reaction

President Donald Trump condemned the shooting as an "act of evil" and called it "horrific."

The President, who was in Japan, said the shooting was caused by a "mental health problem," not an issue with gun laws.

"Mental health is your problem here," Trump said, noting that "based on preliminary reports" the shooter was "a very deranged individual."

"This isn't a guns situation," Trump said. "This is a mental health problem at the highest level. It's a very, very sad event."

Abbott, Texas' governor, said the state would mourn the dead and support their families.

"As governor, I ask for every mom and dad at home tonight, that you put your arm around your kid and give your kid a big hug, and let them know how much you love them," Abbott said at a news conference Sunday evening.

US Sen. John Cornyn of Texas called the news "truly heartbreaking" in a tweet Sunday. "Please say a prayer for First Baptist congregation, first responders & the community there," he said.

Abbott and others attended a vigil Sunday night at the Sutherland Springs post office.

"We have never had this happen before," said Debra Morales, a volunteer coordinating relief efforts for victims' family members. "It's all just very upsetting."