CNN —  

A gunman who wore a mask, bulletproof vest and hearing protection was killed by police within 30 seconds of opening fire on Sunday in a popular nightlife district in downtown Dayton, Ohio, authorities said.

Dayton Police Chief Richard Biehl released a timeline of the early morning shooting that left nine people dead, including the gunman’s sister.

Biehl said the shooter opened fire with a .223-caliber high-capacity rifle with 100-round drum magazines. Officers patrolling the Oregon District as the bars were closing shortly after 1 a.m. heard the gunfire and saw a large crowd running away, the police chief said.

“The officers immediately advanced toward the gunfire and within approximately 20 seconds, they engaged the suspect, who was actively firing and attempting to enter a crowded liquor establishment,” the police chief said.

“The threat was neutralized at approximately 30 seconds of the suspect firing his first shot,” Biehl said.

Biehl released a frantic 911 call from the shooting as well as surveillance footage and the names of the six officers who responded to the shooting. The officers were not injured.

Twenty-seven other people were injured when Connor Betts, 24, fired dozens of shots. The motive remained unclear.

Betts, his sister and a male companion had arrived in the same vehicle but they separated at some point in the evening, the police chief said. Police are trying to determine the shooter’s whereabouts after he and his sister separated.