A man opened fire with an assault weapon at a church near San Antonio, Texas, Sunday morning, killing 26 worshipers and wounding at least 20.
The victims range from five to 72 years old.
The gunman is also dead and there is no clue so far as to his motive.
Federal investigators from the FBI and the Bureau of Alcohol, Tobacco, and Firearms have joined local law enforcement officers in tiny Sutherland Springs, Texas, about 50 kilometers from San Antonio.
On Monday, U.S. President Donald Trump said the mass shooting "isn't a guns situation" but is instead "a mental health problem at the highest level. It's a very, very sad event." He said the shooter was "a very deranged individual." The president is monitoring the situation from Japan, the first stop on his five-nation Asian trip.
Earlier, Trump called the shootings "an act of evil" and appealed for prayers. He ordered U.S. flags on federal buildings to be flown at half-staff through Thursday.
"We cannot put into words, the pain and grief we all feel and we cannot begin to imagine the suffering of those who lost the ones they so dearly loved. Our hearts are broken," the president said.
Worst mass shooting in Texas history
Texas Governor Gregg Abbott says this is worst mass shooting in Texas history. He said there are "many pieces of a complex puzzle" to put together.
What is known, according to Texas public safety official Freeman Martin, is that the gunman, later identified as Devin P. Kelley, was described as a young white male dressed in black and wearing a bullet-proof vest. He first opened fire with an assault rifle outside the First Baptist Church and continued shooting after going inside.
Freeman said a local resident with his own rifle confronted the shooter, causing the gunman to drop his weapon and flee in his car. The citizen pursued the gunman, joined shortly by police. Freeman said the suspect crashed the car just over the county line and was found dead in the vehicle from a gunshot wound. It is unclear if he killed himself or was shot by the citizen.
Wilson County Sheriff Joe Tackitt says police found multiple weapons in the suspect's car.
WATCH: Reactions to Texas attack
Discharged from US Air Force
U.S. Air Force spokeswoman Ann Stefanek told VOA late Sunday that records show Kelley was discharged from the Air Force about three years ago.
"Records checks confirm Devin P. Kelley was previously a USAF member, who served in Logistics Readiness at Holloman AFB, NM, from 2010 until his discharge in 2014. Kelley was court-martialed in 2012 for two counts of Article 128 UCMJ assault on his spouse and assault on their child. Kelley received a Bad Conduct Discharge, confinement for twelve months and a reduction to the grade of E-1," the Stefanek said.
Two of the victims were killed outside the church. The rest were shot inside.
An eyewitness to the shootings, who is a Vietnam War vet, told VOA's Mehtap Colak Yilmaz that he had not seen anything like the church massacre "since Vietnam."
Marie Ann Montgomery, the church's Sunday school director, told VOA's Yilmaz that people in the congregation knew Kelley and some of the suspect's family members were among the victims. Montgomery stopped short, however, of saying the suspect deliberately targeted his family.
While none of the victims have been publicly identified, First Baptist Church Pastor Frank Pomeroy told U.S. news networks that his 14-year-old daughter, Annabelle Renee Pomeroy, is among the deceased.
Pomeroy was in Oklahoma at the time of the shooting. He told ABC News he was on his way back to Sutherland Springs.
?He said all of the people killed Sunday were close friends. Pomeroy also said he wants the world to know his daughter “was one very beautiful special child.”
Caught on camera
Sheriff Tackitt says the church posts its weekly services on YouTube and that the massacre was likely caught on camera. The FBI says it believes only one gunman was involved.
Sunday's Texas shooting comes just weeks after October's mass killing in Las Vegas. Stephen Paddock opened fire on a country music show there, killing 58 and wounding about 500. Paddock shot from his 32nd floor hotel room and killed himself as police moved in. Investigators in the Las Vegas shooting are still working to confirm a motive.
Pentagon Correspondent Carla Babb contributed to this story.