TULSA: The white Tulsa police officer who fatally shot an unarmed black man whose car had broken down and blocked a road was charged with first degree manslaughter on Thursday and a warrant has been issued for her arrest.

Court papers filed by Tulsa County said Officer Betty Shelby escalated the situation and overreacted in shooting Terence Crutcher, 40. If convicted, she faces at least four years in prison, lawyers said.

The incident, captured on police videos, has intensified scrutiny of the use of excessive force by police and claims of racial bias by law enforcement in the United States.

"Although she is charged, she is presumed innocent until a judge or jury determines otherwise," Tulsa County District Attorney Steve Kunzweiler told reporters after an investigation in which more than 50 people were questioned.

In two videos provided by Tulsa police on Monday Crutcher can be seen with his hands in the air shortly before he was shot.

"While we are pleased to learn that the officer who senselessly killed my beloved twin brother is being held accountable for her reckless actions, nothing will bring him back," his sister Tiffany Crutcher told a news conference.

According to an arrest affidavit, Shelby told investigators "that she was in fear for her life and thought Crutcher was going to kill her."

The affidavit said an officer flanking Shelby used a Taser on Crutcher, who was standing facing his vehicle. Then Shelby fired at Crutcher, whose left hand was not clearly in view.

Shelby said she was traveling to another call when she came upon Crutcher. She said he did not respond to her questions and did not respond to her commands to stop as he walked to his vehicle with his hands in the air, it said.

"Officer Shelby acted unreasonably by escalating the situation," the affidavit said, adding that "she became emotionally involved to the point that she overreacted."

Tulsa police have said Crutcher was unarmed and there was no weapon in the vehicle. In a bid for transparency, they released the videos, one of which was taken from a police helicopter and the other from a dashboard camera in a patrol car.

The US Justice Department has launched a separate investigation to see if the officers on the scene violated Crutcher's civil rights.