The state authorities are not yet visible to investigate the killing of Arbery as a hate crime as Georgia does not have a hate crime law.

The United States Department of Justice is weighing up on either to file a hate crime charges against the whites who shot dead Ahmaud Arbery, an unarmed black man who was shot while jogging in the small coastal town of Brunswick, Georgia.

"The Civil Rights Division of the Department of Justice, the FBI, and the US Attorney for the Southern District of Georgia have been supportive and will continue fully to support and participate in the state investigation.

We are carefully assessing all the evidences to determine whether federal hate crimes charges are appropriate," Kupec said in a statement.

State authorities were unable to investigate the killing as a hate crime as Georgia is one of four states without a hate crime law.

Outrage over Arbery's death came through last week after a viral video of the alleged murder, which took place on February 23, surfaced.

The video shows Arbery running at a jogging pace on the left side of a road with a truck parked on the road ahead of him. One white man is inside the pick-up truck's bed, while the other is standing beside the driver's open door.

The runner crosses the road to pass the pick-up truck on the passenger side, then crosses back in front of the truck. A gunshot sounds, and the video shows the runner grappling with a man in the street over what appears to be a shotgun or rifle.

A second shot is heard, and the runner can be seen punching the man. A third shot is fired at point-blank range. The runner staggers a few feet and falls face down.

Authorities asked the Georgia Bureau of Investigation (GBI) to look into the case last week after the video emerged.

The GBI arrested and charged father and son, Gregory and Travis McMichael, with murder and aggravated assault.

The father and son told police they thought Arbery matched the appearance of a burglary suspect who they said had been recorded on a surveillance camera some time before, according to the Glynn County police report filed after the shooting.

Arbery's mother, Wanda Cooper Jones, has said she thinks her 25-year-old son, a former high school football player, was just jogging in the neighbourhood before he was killed.

Meanwhile, a man identifying himself as the person who recorded the mobile phone video of the shooting said he had received death threats.

William "Roddie" Bryan is identified as a witness in the police report taken after Arbery's shooting. He appears to be mentioned in a single sentence of the report, which says Gregory McMichael told an officer that "'Roddy' attempted to block [Arbery] which was unsuccessful."

"I had nothing to do with it. I'm trying to get my life back to normal, and it's been smeared for the last week," Bryan told WJAX-TV in an interview that aired Monday. "I was told I was a witness, and I'm not sure what I am, other than receiving a bunch of threats."

Bryan has not been charged in the case. The TV station reported Bryan would not discuss his involvement in the events that led to Arbery's death.