Dayton police identified the shooter as Connor Betts, 24, from nearby Bellbrook, a small city about 15 miles outside Dayton.
Betts was studying psychology at a local community college and worked at a Chipotle restaurant, according to The Washington Post.
He said he was "Good under pressure. Fast learner, Eager to overachieve" in an online profile, the Post reported.
Police Chief Richard Biehl said while Betts had had several traffic violations, there was nothing in his history, no run-ins with the law or any other criminal behavior, that would indicate he was capable of a mass shooting.
Betts allegedly killed his own sister, Megan Betts, 22, in the attack, police said
Connor Betts drove a 2007 gray Toyota Corolla, according to WHIO, and parked it in a parking lot near Ned Pepper's, the bar he was targeting when he was shot and killed by police before making it inside.
Betts was wearing a mask, body armor and hearing protection when he headed for the bar late Saturday night, WHIO reported.
Betts was armed with a .223-caliber rifle and had double drum magazines that held hundreds of rounds of ammunition, police said.
The gun was ordered online from Texas, and Betts allegedly picked it up from a local Dayton dealer.