The gunman's sister was one of nine people killed in a shooting early Sunday in downtown Dayton, Ohio, police said.
At least 27 others were injured when Connor Betts, 24, fired an assault rifle in a popular nightlife district about 1 a.m., authorities said.
Betts fired for less than a minute from a ".223 high-capacity" gun, and he had additional magazines with him, Mayor Nan Whaley said. The .223 caliber is used in rifles like the AR-15 assault rifle used in previous mass shootings.
Deb Decker, public information officer for Montgomery County, said the shooter used an assault rifle.
The event happened 13 hours after a shooting in El Paso, Texas, left 20 dead.
The Dayton shooting took place on East Fifth Street in the city's Oregon District, Dayton Deputy Director and Assistant Chief of Police Lt. Col. Matt Carper said early Sunday morning.
Local and federal law enforcement sources served a search warrant on Betts' family home in Bellbrook, Ohio. The motive remains unclear.
'A very large gun' and body armor
Betts began shooting as he made his way toward a bar called Ned Peppers, Decker said.
Carper said Betts fired multiple rounds from "a very large gun, in technical terms."
Someone from Ned Peppers grabbed the barrel of the rifle, and the shooter "picked up a handgun and was willing to continue shooting," Decker said, when police arrived and killed the shooter.
The shooter wore body armor, she said.
No officers were injured, Carper said.
"In less than one minute, Dayton first responders neutralized the shooter," Whaley said.
"I really want to -- think about that minute. The shooter was able to kill nine people and injure 26 in less than a minute. And if we did not have police in the Oregon District and the thousands of people in the Oregon District enjoying their Saturday evening, what we could have had in this city," she said.
"The question has to be raised, why does Dayton have to be the 250th mass shooting this year?"
The gunman's victims
The city identified the nine people killed in the shooting:
Police did not provide information about the Betts siblings' relationship.
'Bodies all over the place'
Graham Hunter, 24, of Dayton said he and four friends arrived just as the incident was over and immediately came upon the body of the shooter outside.
"Everyone was panicking and running around," Hunter said. "After the shooter was dead, everyone was just crying and stuff," and he saw "bodies all over the place."
A police officer told him and his friends to go into Ned Peppers.
He said he and his friends consider the area a safe, fun place to hang out on weekends, where many people walk around outdoors and enjoy patios at restaurants and bars.
"It's a nice spot," he said. "It's where everyone goes to hang out."
The district will be open Sunday afternoon, the mayor said.
A vigil is planned for 8 p.m. ET Sunday.
A deadly end to a deadly week in America
The shooting in Dayton was the fourth similar incident across the country in the past week. At least 34 people were killed in total.
Saturday morning In El Paso, 20 people were killed and 26 injured when a gunman opened fire at a shopping center. Authorities are investigating a racist, anti-immigrant scree they believe was posted by the suspect.
He has been identified by three sources as Patrick Crusius, a 21-year-old white man from Allen, Texas.
Tuesday in Mississippi, a shooting at a Walmart left two employees dead and a police officer wounded.
On July 28, when a 19-year-old man wearing tactical gear opened fire at at the Gilroy Garlic Festival in California, killing three people, including two children.
Friend recalls 'really nice kid'
A friend, Brad Howard, said Connor Betts was quiet and kept to himself.
"He was a really nice kid," Howard told CNN affiliate WHIO . The two grew up together, he said, and knew each other for more than 20 years.
The friends would talk music and pop culture, he said.
"It's a kick in the teeth" to the Bellbrook neighborhood, Howard said.
Hospitals respond to influx of wounded
The mayor said 27 people were treated at hospitals and 15 had been released by about 10 a.m. ET Sunday.
Elizabeth Long, spokeswoman at Kettering Health Network, which operates several Dayton-area hospitals including Kettering Medical Center and Grandview Medical Center, said 13 people were taken to three of the network's hospitals, many with gunshot wounds to the "lower extremities."
At least one person was shot in the abdomen, and at least two people were taken into surgery. She did not give an age range for the injured.
Miami Valley Hospital received 14 patients, plus two others across its health system, emergency physician Dr. Randy Marriott said. Twelve had been treated and released by 10 a.m. ET Sunday.
Most of the injuries were gunshot wounds, but there were others, like cuts received while people were fleeing the scene.
"At this point, we can say we've had one critical, four admitted, none have gone to surgery," Marriott said.
Most people arrived via ambulance or police car, but several others arrived on foot or by personal vehicle later, Marriott said.
Congressman's daughter was in the area
Dayton-based US Rep. Mike Turner tweeted that his daughter and a friend had just entered a bar across the street when the shooting began. "As they ran home, I followed their progress & prayed for them & our community. Thank you to @DaytonPolice for their bravery in stopping this evil."
Gov. Mike DeWine said in a statement that he was "absolutely heartbroken" and ordered flags flown at half-staff.
US Rep. Marcia Fudge, D-Ohio, tweeted, "It is beyond time for our leaders to do what is necessary to enact laws that keep guns out of the hands of people wishing to do harm. This has to stop . #EnoughIsEnough #EndGunViolence"
President Donald Trump tweeted, "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!"