Dallas police are pursuing a manslaughter case against one of their own officers after she shot and killed her neighbour, officials said on Friday.

The unnamed officer thought 26-year-old Botham Jean's flat was her own when she entered, according to police.

She had walked into the flat following her shift on Thursday and then called police, saying that she had shot a man. Officials said that the officer's blood was being tested for drugs and alcohol.

Jean was taken to hospital where he later died.

It is unclear what happened immediately before the shooting. Officials said that they do not know how the officer got into Jean's home, or whether the front door was open or unlocked.

"Right now, there are more questions than we have answers," Dallas police chief U Renee Hall said at a press conference.

Hall said she did not know where the officer was. It is unclear whether she is in custody.

Jean worked for accountancy giant PricewaterhouseCoopers, which said that people at the firm were "heartbroken" following his death.

Jean grew up in St Lucia and was a graduate of Harding University in Arkansas, where he was known for his love of singing and for leading services in the university chapel.

"Botham was in the prime of his life," Ignatius Jean, Jean's uncle, said.

He added that the killing had left Jean's relatives in St Lucia devastated and that Jean was a "brilliant" man of "impeccable character".

"You want to think it's fiction... and you have to grapple with the reality", he said.

The Texas Rangers, a department which investigates crime across the state, will conduct an independent investigation into Jean's death, police said.