A Dallas police officer returning home from work shot and killed a neighbor after she said she mistook his apartment for her own, authorities said on Friday.

The officer called dispatch to report that she had shot the man on Thursday night, police said. She told responding officers that she believed the victim’s apartment was her own when she entered it.

The responding officers administered first aid to the victim, whom the Dallas county medical examiner’s office identified as 26-year-old Botham Jean. He was taken to a hospital and pronounced dead.

Police have not released the name of the officer, who was not injured. She will be placed on administrative leave pending the outcome of the investigation, police said.

Authorities have not said how the officer got into Jean’s home, or whether his door was open or unlocked. The apartment complex is just a few blocks from Dallas’s police headquarters.

At a Friday morning news conference, Sgt Warren Mitchell acknowledged there were many questions about what happened that he could not answer.

"We still have a lot to do in this investigation. So there’s a lot of information I understand you guys want but this is all we can give you at this time," Mitchell said.

When asked if anyone else had witnessed the shooting, Warren replied: "We have not spoken to anyone else at this time."

Residents of the apartment complex said they can access their units with a regular key or through a keypad code.

Two women who live on the second floor near where the shooting happened said they heard a lot of noise late on Thursday.

"It was, like, police talk: ‘Open up! Open up!’" 20-year-old Caitlin Simpson told the Dallas Morning News.

Yazmine Hernandez, 20, was studying with Simpson when they heard the commotion.

"We heard cops yelling, but otherwise had no idea what was going on," Hernandez said.

Tomiya Melvin, who moved from Chicago to a nearby apartment complex in June, said she found out about the shooting while she was walking her dog on Friday morning.

"It’s terrible. I hope it’s just a tragic accident and nothing more than that," Melvin said.

Police said they are conducting a joint investigation with the Dallas county district attorney’s office.