WASHINGTON (REUTERS) - One of the white men charged in the Georgia killing of Ahmaud Arbery used a racial slur after shooting the unarmed black man, an investigator for the prosecution said in court on Thursday (June 4), an explosive new allegation in one of the cases roiling race relations in the United States.

After hearing arguments from attorneys for the prosecution and the defense, Glynn County Chief Magistrate Judge Wallace Harrell ruled the prosecution met the probable cause threshold and sent the case to a superior court for trial.

Special Agent Richard Dial of the Georgia Bureau of Investigation said William Bryan told his office in an interview last month that Travis McMichael uttered the slur after shooting Arbery.

Bryan and McMichael are both defendants in the case.

"Mr Bryan said that after the shooting took place before police arrival, while Mr Arbery was on the ground, that he heard Travis McMichael make the statement: f***ing n****r," Dial said in testimony.

The Arbery case triggered a national outcry after cellphone video of the Feb 23 shooting was leaked on social media.

Thursday's hearing was to determine if there is enough evidence for the case to go to trial.

The hearing in Glynn County follows more than a week of demonstrations across the United States over the May 25 death in Minneapolis police custody of George Floyd, also a black American.

Four officers have been charged in that case.

Dial said he had evidence from social media and elsewhere that Travis McMichael had used racial slurs in the past.

McMichael, a former US Coast Guard boarding officer, once told a friend that he loved his job because he "was on a boat and there weren't any N-words anywhere," Dial testified.

Dial said the three defendants - Bryan, 50, Travis McMichael, 34, and his father Gregory McMichael, 64 - chased Arbery in pickup trucks and sought to box him in as he was jogging in their neighbourhood.

Both McMichaels are charged with murder and aggravated assault. Bryan, their neighbour who took the cellphone video, was charged with murder and attempting to illegally detain and confine.

Jason Sheffield, an attorney for Travis McMichael, pressed Dial on whether Bryan was promised leniency for possible cooperation with prosecutors when he cited the alleged slur and whether he had evidence his client acted in self defence.

Dial said he was unaware of any leniency offer and that it was Arbery, not McMichael, who was defending himself.

"I believe Mr Arbery's decision was to just try to get away and when he felt like he could not escape, he chose to fight."

Dial also testified that investigators found several texts on Bryan's phone that contained racially derogatory comments, and that he believed racial bias played a role in Bryan's decision to join the pursuit of Arbery.

The three defendants were not charged until more than two months after the shooting. State police stepped in to investigate after the video circulated widely and Glynn County police took no action.

Police say Gregory McMichael saw Arbery running in his neighbourhood and believed he looked like a burglary suspect. The elder McMichael called his son and the two armed themselves and gave chase in a pickup truck, police say.

Dial said video and other evidence showed that the first of three shots from Travis McMichael's 12-gauge Remington Model 870 pump-action shotgun was to Arbery's chest.

"You see the front of his shirt is saturated with blood," Dial said.

"The second shot is off camera as well but you do see the blood mist come into the camera screen."