9 killed in Dayton, Ohio, in second U.S. mass shooting in 24 hours

(CNN) – 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 followed by 13 hours a shooting that left 20 dead in El Paso, Texas.

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.

During the search, authorities found writings linked to the shooter that show he had an interest in killing people, two federal law enforcement sources told CNN. A preliminary assessment of the writings did not indicate any racial or political motive, the sources said.

"We're always looking at what could have motivated such a horrific action as this, and like I said this morning, we're interviewing dozens of people and going through a lot of different electronic evidence, other evidence to try to determine that. We don't have that answer yet," Carper said. "But speculating at this point would be premature."

'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 shooting in Dayton was the fourth similar incident across the country in the past week. At least 34 people were killed in total.

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!"

Saturday morning In El Paso, 20 people killed and 26 injured when a gunman opened fire at a shopping center. Authorities are investigating a racist, anti-immigrant screed 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.