The Department of Justice said it will not be pursuing charges against a former police officer who shot and killed an unarmed black man.

On Friday, US Attorney Trent Shores announced the closure of the investigation into whether Betty Shelby used unreasonable force against Terence Crutcher, an African-American man, when she shot him dead in September 2016.

"The Department of Justice devoted significant resources to this investigation to ensure that a thorough review was undertaken,” Mr Shores said in a statement. “Attorneys from both the Civil Rights Division and the US Attorney's Office worked closely with the FBI to examine the evidence and review applicable law.”

In May 2017, a Tulsa County jury acquitted Ms Shelby for fatally shooting Mr Crutcher. Mr Crutcher held his hands over his head when she shot him.

However, Ms Shelby testified she fired her gun out of fear, claiming Mr Crutcher did not listen to her commands. She claimed that when Mr Crutcher – who was unarmed – reached into his SUV, she thought he was reaching for a gun.

Black Lives Matter organises march to Trump Tower Show all 15 1 /15 Black Lives Matter organises march to Trump Tower Black Lives Matter organises march to Trump Tower Kandy Freeman participates in a Black Lives Matter protest in front of Trump Tower in New York City, U.S. January 14, 2017. Stephanie Keith/Reuters Black Lives Matter organises march to Trump Tower People participate in a Black Lives Matter protest in front of Trump Tower in New York City, U.S. January 14, 2017. Stephanie Keith/Reuters Black Lives Matter organises march to Trump Tower Hawk Newsome, a Black Lives Matter activist, leads a protest outside Trump Tower in New York City on January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower Hawk Newsome (C) leads a chant during a Black Lives Matter protest in front of Trump Tower in New York City, US. January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower People participate in a Black Lives Matter protest in front of Trump Tower in New York City, U.S. January 14, 2017. Stephanie Keith/Reuters Black Lives Matter organises march to Trump Tower An NYPD officer speaks with a Black Lives Matter leaders during a protest in the snow outside Trump Tower in New York City on January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower Kandy Freeman participates in a Black Lives Matter protest in front of Trump Tower in New York City, U.S. January 14, 2017. Stephanie Keith/Reuters Black Lives Matter organises march to Trump Tower An NYPD officer speaks with a Black Lives Matter leaders during a protest in the snow outside Trump Tower in New York City on January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower Carol Garza, a Black Lives Matter supporter, protests outside Trump Tower in New York City on January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower People participate in a Black Lives Matter protest in front of Trump Tower in New York City, U.S. January 14, 2017. Stephanie Keith/Reuters Black Lives Matter organises march to Trump Tower A Black Lives Matter supporter protests in the snow outside Trump Tower in New York City on January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower Black Lives Matter activists march in front of Trump Tower on January 14, 2017 in New York City. Kevin Hagen/Getty Black Lives Matter organises march to Trump Tower Black Lives Matter activists march in front of Trump Tower on January 14, 2017 in New York City. Kevin Hagen/Getty Black Lives Matter organises march to Trump Tower Black Lives Matter supporters protest in the snow outside Trump Tower in New York City on January 14, 2017. Dominick Reuter/AFP/Getty Images Black Lives Matter organises march to Trump Tower Black Lives Matter Kandy Freeman marches in front of Trump Tower on January 14, 2017 in New York City. Kevin Hagen/Getty

"We're disappointed, but unfortunately we're not surprised," Demario Solomon-Simmons, an attorney for Mr Crutcher's family, told the Associated Press. "The number one reason is that the system is set up to protect officers like Betty Shelby. The standard (of proof) is so high, it's the highest standard in the legal system, to prove that someone willfully and intentionally violated someone else's civil rights."

Following her acquittal, Ms Shelby resigned from her position at Tulsa Police Department.

Mr Crutcher’s family filed a federal lawsuit against the City of Tulsa and Ms Shelby. The suit is still pending in federal court.

Mr Shores said a team made up of Justice Department prosecutors and FBI agents examined all the evidence in Mr Crutcher’s case, including enhanced video footage of the shooting, to determine whether Ms Shelby “willfully” violated federal law and required the team to determine that she acted with “deliberate and specific intent” to do something illegal.

Support free-thinking journalism and attend Independent events

"Any allegation of law enforcement misconduct and willful deprivation of civil rights is taken seriously," Mr Shores said.