DAYTON, Ohio — The police on Monday were still trying to determine what motivated a gunman in Dayton to kill his sister and eight others, but people who grew up with him were conducting a different kind of investigation, looking back for any signs that might have foreshadowed his explosion of violence.

For more than a few, and for women in particular, these signs were not hard to find.

“I don’t want to say I saw it coming,” said Mika Carpenter, 24, who met the gunman, Connor Betts, 24, at a summer camp when they were both 13. “But if it was going to be anybody it was going to be him.”

Like others who knew Mr. Betts as a teenager, Ms. Carpenter recalled his dark and often violent jokes, including riffs about “bodily harm” that led many to keep their distance.

“He was kind of hateful to women because they didn’t want to date him,” she said. Still, she became friends with him because, she said, she saw that he had a good side.