“We didn’t know anything, absolutely anything, until like 3:30 a.m.,” Ms. Looney said.

Hannah’s death is one of the most recent shootings to raise questions about police officers’ use of lethal force , has left her family wondering what happened between when Hannah was last seen and when she was killed. The Fullerton police officer has not been named, but authorities said he was on duty and in uniform. He was taking a police dog to a veterinarian when he crossed paths with Hannah, they said.

But many details, including what led to the shooting, are not clear.

The Orange County District Attorney’s Office, which is investigating the shooting, said Tuesday that a replica handgun had been found near Hannah at the scene. But it declined to provide any further details, including specifically where the replica handgun was found or how, if at all, it might have figured in the deadly encounter.

Hannah’s parents, however, cannot reconcile the news with the daughter they knew, who this summer started her first job as a lifeguard at a theme park, Knott’s Berry Farm; had been voted captain of her soccer team at Magnolia High School; and liked volunteering at events to support veterans.

“I still don’t believe it,” said Benson Williams, Hannah’s father. “I still think she’s going to knock on the door, she’s going to call.”

He added, “We didn’t get to say goodbye to her.”

Police shootings have drawn heightened attention nationwide, but Hannah’s death comes as discourse in California has been particularly heated.