(CNN) A white Tulsa, Oklahoma officer charged in the shooting death of an unarmed black motorist last year said race was not a factor in her decision to open fire. She said the man "caused" his death when he ignored her commands, reaching into his vehicle to retrieve what she believed was a gun.

"I saw a threat and I used the force I felt necessary to stop a threat," Officer Betty Shelby said Sunday during an interview on 60 Minutes.

Shelby is scheduled to stand trial next month on a felony manslaughter charge in the fatal shooting of Terence Crutcher, 40, on September 16.

In her first public comments since her arrest, Shelby said Crutcher kept putting his hands in his pockets. He didn't stop moving when she ordered him to, she said, and he appeared to be sizing her up before reaching into the vehicle. She said feared for her life.

"I have sorrow that this happened, that this man lost his life, but he caused the situation to occur," she said. "So, in the end he caused his own (death)."

Crutcher's sister: The officer 'didn't pause'

In a grainy video taken from a police helicopter, Crutcher can be seen walking away from Shelby toward his vehicle with his arms in the air before he was shot. No weapon was found in Crutcher's vehicle.

The shooting has sparked investigations by the Justice Department and state authorities.

Shelby has pleaded not guilty . If convicted of first-degree manslaughter, she faces a sentence of four years to life, according to Susan Witt, the spokeswoman for the district attorney's office.

The criminal complaint against Shelby alleges that her "fear resulted in her unreasonable actions which led her to shooting" Crutcher. She is accused of "unlawfully and unnecessarily" shooting him after he did not comply with her "lawful orders."

Crutcher's twin sister, Tiffany Crutcher, said her brother didn't pose a threat.

Police Officer Betty Shelby has been charged with felony manslaughter.

"What we saw on that video is what my dad always taught us to do if we were pulled up by a police officer: put your hands in the air and put your hands on the car," she said. "And my brother did what my father taught us."

She said her brother died because Shelby "didn't pause."

"And because she didn't pause, my family, we've had a pause," she said. "We've had to stop. We've had to lay down every single night with tears in our eyes."

She added: "There was absolutely no justification whatsoever, with all the backup, for Officer Shelby to pull that trigger."

Crutcher's behavior was 'zombie-like,' officer says

Shelby's 60 Minutes interview mirrors what her attorney has previously said.

In the interview, she argued that there was justification for her actions, describing an encounter that was not captured on video.

Shelby was on her way to a domestic violence call when she saw a man she would later learn was Crutcher standing in the road, the officer told 60 Minutes. She said she found the 6-foot, 240-pound man's behavior concerning.

"His hands are just dropped beside him, his chin is resting on his chest, and he's standing there motionless," she said. "I thought ... I wonder if he's on PCP."

She described Crutcher's behavior as "zombie-like."

An autopsy found Phencyclidine, or PCP, in Crutcher's system at the time of his fatal shooting, according to the toxicology report released with his autopsy by the Oklahoma Chief Medical Examiner's Office. The report did not indicate when the drug entered his system.

Shelby said she continued driving and encountered an abandoned SUV in the middle of the road. She said she didn't activate her dash camera because she thought it was just a broken-down vehicle.

But she noticed the SUV's motor was running and the windows were down. Suspicious, Shelby said she looked inside to see if anyone was hurt.

She then saw Crutcher walking toward her and the vehicle. She asked him if the vehicle was his, but he mumbled something incoherent and put his hands his pocket, she said.

He immediately put his hands in the air when she ordered him to take his hands out of his pocket, Shelby said.

"I've encountered people putting their hands in their pockets and I find a loaded gun in their pocket," she said.

Officer: 'Race had nothing to do' with shooting

Shelby said Crutcher was not belligerent and showed no aggression.

"Is it possible that you saw him as more dangerous because he was a large black man?" correspondent Bill Whitaker asked.

Shelby said her actions were only based on Crutcher's actions and behavior.

"Race had nothing to do with my decision-making," she said.

She said Crutcher ignored her orders to get on his knees and continued walking to the SUV, even though she had drawn her weapon. She said that, with his hands still in the air, he kept looking back at her and at the vehicle. She said she believed Crutcher would harm her.

She said she felt Crutcher was "calculating how he can get to his vehicle to get whatever weapon it is that he's going to get because he didn't find it in his pocket."

Shelby said that as he got near his vehicle, "his shoulders drop, his arm drops and he's reaching in ... It's fast."

"I say with a louder, more intense voice 'stop, stop, stop,' and he didn't," she said. 'And that's when I took aim."

Shelby said she "could very well be dead" if she had waited to find out if Crutcher had a gun.

"There's something that we always say, 'I'd rather be tried by 12 than carried by six,'" she told Whitaker.

'My brother is another hash tag'

Crutcher's death was one of many high-profile shootings of African-American men by police nationwide in recent years, including the shooting death of Philando Castile in July in Minnesota. The shootings have led to protests and given further momentum to the national conversation about race and policing

Crutcher was a hard-working Tulsa Community College student and the father of four girls. His sister told Whitaker he was "laid back, calm, cool."

"Gospel music was his love," she said.

"I saw Trayvon Martin. I saw Mike Brown. I saw Philando Castile. I saw Tamir Rice," Tiffany Crutcher said. "But never in a thousand years ... would we have thought that we would be on their side of it. And my brother now, according to social media, is another hash tag."