"You didn't hear the officer shout, 'Gun, gun, gun,"' attorney Lee Merritt said after viewing video from a Fort Worth officer's bodycam during Saturday's shooting of Atatiana Jefferson, 28.

"He didn't have time to perceive a threat. That's murder."

Ms Jefferson's family told KXAS television she was watching her 8-year-old nephew when she was killed.

Fort Worth Police Department said in a statement officers saw someone near a window inside the home and one of them drew his duty weapon and fired after "perceiving a threat".

The video released by police shows two officers searching the home from outside with torches before one shouts, "Put your hands up, show me your hands".

One shot is then fired through a window.

"It's another one of those situations where the people that are supposed to protect us are actually not here to protect us," said Jefferson's sister, Amber Carr.

"You know, you want to see justice, but justice don't bring my sister back," she said.

An aunt, Venitta Body, said the family does not understand why Jefferson was killed.

"It's like from the moment we got the call, it's been more and more inconceivable and more confusing."

Police Lieutenant Brandon O'Neil said on Sunday the officer, who's been on the force since April 2018, is on leave pending an investigation.

He will be interviewed about the fatal shooting on Monday. His name was not released.

O'Neil confirmed the officer did not announce he was a policeman before he fired the fatal shot and his failure to do so is part of the department's investigation.

He also said Jefferson's 8-year-old nephew was in the room when Jefferson was shot.

James Smith, who called a police non-emergency number about Ms Jefferson's door being open, told reporters he was just trying to be a good neighbour.

"I'm shaken. I'm mad. I'm upset. And I feel it's partly my fault," he said. "If I had never dialled the police department, she'd still be alive."

Australian Associated Press