“Had this individual made it through the doorway of Ned Peppers with that level of weaponry, there would have been a catastrophic injury and loss of life, so stopping him before he got inside there — you saw all those people were running in there — was essential,” Mr. Biehl said.

No manifesto or social media presence has been found so far for Mr. Betts.

The police said they are treating Mr. Betts’ family like other victims given that they have lost their daughter.

A neighbor remembered the gunman making threats during his high school years.

Theo Gainey, 25, who lived for 10 years down the block from the Bettses and was a year ahead of Connor Betts in school, remembered him as a “bit of an outcast,” ostracized in large part because of threats he made at school that got him into serious trouble.

“He got arrested on the school bus” for the threats, said Mr. Gainey, who added that he was on the bus himself when it happened. He recalled Mr. Betts being a freshman or sophomore at the time. Mr. Gainey did not remember the specifics of the threats but said that Mr. Betts had to leave school for the rest of that year. When he returned, “the threat thing followed him, and people didn’t want to hang out with him.”

The suspect’s family home was searched.

BELLBROOK, Ohio — The police searched a house in a quiet suburb southeast of Dayton early Sunday morning, where the man identified by the officials as the gunman lived with his parents.

The house is on a cul-de-sac that had been blocked on Sunday with temporary barriers, a strange sight in a neighborhood of otherwise peaceful homes of freshly mowed lawns and people doing yard work.

“Just like everybody else in the world, you don’t expect it to be a few blocks from your place,” said Brian Harris, who was standing up the street with his wife, Diane; they own a machine shop. “This is one of the safest places,” Ms. Harris said.