Surveillance footage shows another angle, with people scrambling to get in the bar to get away from him moments earlier. Police shot and killed him within seconds, right by the entrance. He had already killed nine people.
Dylan Arnold, who took the bystander video, said he didn't have time to react.
"It happened so fast. No one prepares you for how fast they happen," he said. "You think you have time to react. You're going to do something cool, something macho, but you don't. Because it's three seconds and you're gone."
Ohio Gov. Mike DeWine said he'll outline his proposals to deal with gun violence and mental health in detail on Tuesday, a little more than a day after hundreds of people chanted "Do something!" while he spoke at a vigil for those killed.
RELATED: President Trump addresses weekend's shootings in El Paso, Dayton
Authorities have identified the adults killed at around 1 a.m. Sunday as:
- Lois Oglesby, 27
- Megan Betts, 22
- Saeed Saleh, 38
- Derrick Fudge, 57
- Logan Turner, 30
- Nicholas Cumer, 25
- Thomas McNichols, 25
- Beatrice Warren-Curtis, 36
- Monica Brickhouse, 39
Hundreds of people, mostly young adults, gathered Sunday evening at the scene in Dayton's Oregon District. They sang "Amazing Grace" and erupted in cheers at the mention of emergency responders who had rushed to the scene.
The suspected gunman, 24-year-old Connor Stephen Betts, of Bellbrook, Ohio, was fatally shot by responding officers within 30 seconds, according to police. Authorities said Betts' sister, Megan, is among the deceased victims.
Police Chief Richard Biehl said any attempt to identify a motive this early in the investigation would be irresponsible.
Dayton Mayor Nan Whaley said the white shooter was wearing body armor, carrying a .223-caliber rifle and had additional high-capacity magazines with him.
After police said there was nothing in his background that would have prevented him from buying the gun, accounts from classmates emerged of a "hit list" and "rape list" that Betts had in high school.
RELATED: Connor Stephen Betts, identified as Dayton suspected shooter, had 'hit list,' 'rape list,' classmates say
This was the second mass shooting in the U.S. in less than 24 hours, following a mass shooting at a Walmart in El Paso, Texas, that left 21 dead.
Dayton police patrolling the area responded in less than a minute to the shooting, which unfolded on the streets outside of Ned Peppers in the Oregon District, Whaley said at a press conference.
Whaley said "hundreds of people in the Oregon District could be dead today" if the police had not responded so quickly.
At a press conference Monday morning, Dayton Fire Chief Jeffrey Payne said 37 people were treated for injuries at hospitals and 11 of them remain hospitalized. Several more remain in serious or critical condition, local hospital officials said at a news conference. They said some people suffered multiple gunshot wounds, and others were injured as they fled.
Nikita Papillon, 23, was across the street at Newcom's Tavern when the shooting started. She said she saw a girl she had talked to earlier lying outside Ned Peppers Bar.
"She had told me she liked my outfit and thought I was cute, and I told her I liked her outfit and I thought she was cute," Papillon said. She herself had been to Ned Peppers the night before, describing it as the kind of place "where you don't have to worry about someone shooting up the place."
"People my age, we don't think something like this is going to happen," she said. "And when it happens, words can't describe it."
Tianycia Leonard, 28, was in the back, smoking, at Newcom's. She heard "loud thumps" that she initially thought was someone pounding on a dumpster.
"It was so noisy, but then you could tell it was gunshots and there was a lot of rounds," Leonard said.
Staff of an Oregon District bar called Ned Peppers said in a Facebook post that they were left shaken and confused by the shooting. The bar said a bouncer was treated for shrapnel wounds.
President Trump tweeted about the quick response of law enforcement at the shootings in Dayton and El Paso.
The FBI, local and state law enforcement are working together in El Paso and in Dayton, Ohio. Information is rapidly being accumulated in Dayton. Much has already be learned in El Paso. Law enforcement was very rapid in both instances. Updates will be given throughout the day!— Donald J. Trump (@realDonaldTrump) August 4, 2019
God bless the people of El Paso Texas. God bless the people of Dayton, Ohio.— Donald J. Trump (@realDonaldTrump) August 4, 2019
He has also declared flags to remain at half-staff until sundown Aug. 8.
VIDEO: Eyewitness captures moment shots rang out in Dayton's Oregon Historic District
Gov. Mike DeWine issued his own statement, announcing that he ordered flags in Ohio remain at half-staff and offering assistance to Whaley and prayers for the victims.
"Fran and I are absolutely heartbroken over the horrible attack that occurred this morning in Dayton," the statement said. "We join those across Ohio and this country in offering our prayers to victims and their families."
Whaley said she has been in touch with the White House, though not Trump directly, and with DeWine. She said more than 50 other mayors also have reached out to her.
The FBI is assisting with the investigation.
With a population of around 140,000 Dayton is in western Ohio, around 55 miles northeast of Cincinnati, 75 miles west of Columbus and 120 miles east of Indianapolis. The Oregon District is a historic neighborhood near downtown Dayton that's home to entertainment options, including bars, restaurants and theaters.
A family assistance center was set up at the Dayton Convention Center, where people seeking information on victims arrived in a steady trickle throughout the morning, many in their Sunday best, others looking bedraggled from a sleepless night. Some local pastors were on hand to offer support, as were comfort dogs.
The Ohio shooting came hours after a young man opened fire in a crowded El Paso, Texas, shopping area, leaving 20 dead and more than two dozen injured.
Just days before, on July 28, a 19-year-old shot and killed three people, including two children, at the Gilroy Garlic Festival in Northern California.
Sunday's shooting in Dayton is the 22nd mass killing of 2019 in the U.S., according to the AP/USA Today/Northeastern University mass murder database that tracks homicides where four or more people were killed - not including the offender. The 20 mass killings in the U.S. in 2019 that preceded this weekend claimed 96 lives.
Whaley said the Oregon District is expected to reopen Sunday afternoon, and a vigil is planned Sunday evening. The minor league Dayton Dragons who play in nearby Fifth Third Field postponed their Sunday afternoon game against the Lake County Captains "due to this morning's tragic event."
The shooting in Dayton comes after the area was heavily damaged when tornadoes swept through western Ohio in late May, destroying or damaging hundreds of homes and businesses.
"Dayton has been through a lot already this year, and I continue to be amazed by the grit and resiliency of our community," Whaley said.
The Associated Press contributed to this report.