By Brendan O’Brien

(Reuters) – A gunman who killed nine people in Dayton, Ohio earlier this month spent two hours in the nightlife neighborhood before unleashing an attack on bar-goers and probably carried it out alone, police said on Tuesday.

The Aug. 4 attack, which ended when police shot and killed the gunman, 24-year-old Connor Betts, was one of three high- profile mass shootings over three weeks that stunned the United States and stoked its long-running debate on gun rights.

During an afternoon news conference, Dayton Police Chief Richard Biehl used footage from video cameras from several businesses in the neighborhood to lay out a detailed timeline of the gunman’s movements around the neighborhood known for its nightlife before the early Sunday morning shooting.

At 11:04 p.m., Betts arrived in his car with his sister and a companion. The trio went to a tavern known as Blind Bob’s. Some 69 minutes later, Betts left the bar alone and went to Ned Pepper’s, a bar across the street, Biehl said as he showed the footage.

Betts stayed at Ned Pepper’s for 28 minutes before heading back to his car, where he spent nine minutes. He changed his clothes, got his AR-15 semi-automatic rifle, body armor and a mask and placed some of the items in a backpack.

Twenty minutes later at 1:04 a.m., two hours after he arrived in the neighborhood, he went back to Ned Pepper’s and opened fire outside the bar, shooting 17 people and killing nine, including his sister, Biehl said.

It is a “strong probability” that Betts went into Ned Pepper’s beforehand to case the establishment, Biehl said.

“He was very familiar with the Oregon District,” he said. “This was a plan well before he got to the Oregon District.”

Biehl said the video footage indicated that Betts acted alone that night.

“Clearly, that day during that time period, we don’t see anyone assisting in committing this horrendous crime,” he said.

The investigation also “seems to strongly suggest” that his companion, who was wounded in the rampage, did not know Betts was planning to carry out the shooting or that he had weapons in the vehicle.

But investigators “have radically different views” on whether Betts targeted his sister and his companion.

“Based on what we know now, we cannot make that call conclusively,” Biehl said.

The FBI said last week that Betts had a history of violent obsessions and had mused about committing mass murder before his rampage in Dayton’s historic downtown.

(Reporting by Brendan O’Brien in Chicago; Editing by Cynthia Osterman)