(CNN) The US Department of Justice announced Friday there wasn't enough evidence to "pursue federal criminal civil rights charges against" a former Tulsa, Oklahoma, police officer who shot an unarmed black man in 2016.

Former Officer Betty Shelby shot and killed Terence Crutcher, 40. Shelby, who is white, said she fired out of fear when she killed Crutcher, who had his hands above his head. She was acquitted of manslaughter in May 2017 and resigned from the department in August 2017.

The Justice Department said in a news release Friday "the federal review sought to determine whether Shelby violated federal law by willfully using unreasonable force against Crutcher." Federal investigators ultimately determined there wasn't enough evidence to "prove beyond a reasonable doubt" that Shelby's use of force was "objectively unreasonable" under the Supreme Court definition. This means there's no evidence to show that Shelby violated Crutcher's constitutional rights with "deliberate and specific intent" to do something illegal.

The release also says investigators couldn't find evidence to refute Shelby's claim that she fired in self-defense believing that Crutcher was reaching into his vehicle to get a weapon.

Damario Solomon-Simmons, attorney for Crutcher's family, said, "We're disappointed, but unfortunately we're not surprised."

"The system is set up to protect officers like Betty Shelby," Solomon-Simmons said. "The standard is so high, it's the highest standard in the legal system, to prove that someone willfully, intentionally violated someone else's civil rights."

Tiffany Crutcher, Terence Crutcher's twin sister, said she wanted the community to know the family wasn't defeated.

"We're standing strong and we're moving forward with our plans and for close to 900 days, we've been fighting for justice and the fight for justice continues," she said.

Shelby's attorney, Shannon McMurray, told CNN affiliate KJRH-TV her client was relieved with the Justice Department's decision.

"I have always believed with proper investigation and looking at all the facts and circumstances, Officer Shelby would be cleared, by a jury and now the Department of Justice," she said.

How the shooting took place

On September 16, 2016, two 911 calls brought officers to the scene.

One of the calls from a woman who said an abandoned vehicle was blocking the street and a man was running away, warning that it was going to blow up.

Video from a police helicopter circling above shows Terence Crutcher with his hands up as an officer approaches him.

Shelby was the first to arrive, but she wasn't responding to the 911 call, said her attorney, Scott Wood. Shelby was en route to a domestic violence call when she encountered Crutcher, who she thought might be impaired, and then the SUV in the middle of the road, Wood said.

She asked Crutcher whether the car belonged to him but got no response, the attorney said. Crutcher began walking toward her with his hands in his pockets. She politely asked Crutcher to take his hands out of his pockets while they were speaking, Wood said.

Crutcher continued to ignore Shelby's questions about the vehicle and at one point walked toward the back of the police cruiser and puts his hands back in his pockets, the attorney said. Shelby called dispatch and was intent on arresting him because she thought he was under the influence of something, he said.

Video from a police dashcam shows Terence Crutcher with his hands up as he walks toward his vehicle.

She drew her gun and ordered Crutcher to get on his knees, which he refused to do, Wood said. He instead walked toward his car.

Police videos show Shelby and several other officers at the scene. There were multiple angles of the shooting including dashcam video and video from a helicopter.

Footage from multiple police cameras show Crutcher walking toward his SUV in the middle of the road, hands raised, followed closely by Shelby and three other officers. They approach Crutcher, who continued to walk back to his car, where he appeared to move his hands toward the vehicle.

Circling above the scene, one police officer in the helicopter can be heard referring to Crutcher as a "bad dude."

Jeanne MacKenzie, Tulsa police spokeswoman, said that the responding officers on the ground thought Crutcher had reached into the driver's side window of the vehicle.

Moments later, as Crutcher stands beside his vehicle, the video shows him fall to the ground.

"I think he may have just been Tasered," an officer says over the radio.

"Shots fired!" a female officer says.

In the video, Crutcher lies in the middle of the street, motionless with blood on his shirt.

It was later found that Crutcher was unarmed.

Aftermath of the shooting

Tiffany Crutcher said in 2016 that a month before the shooting, she and her brother celebrated their 40th birthday. She described her brother as a God-loving father of four who sang at church every week and had enrolled at a community college in Tulsa, where he hoped to earn a degree.

During Friday's news conference, Tiffany Crutcher announced she and other organizations in Tulsa would be holding public hearings in reference to the Tulsa Equality Report , which examines equality in the city.

"Blacks in Tulsa are five times more likely to be victims of use of force and two times more likely to be arrested and we don't know why. We want to know why," she said.