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 has told a court – an explosive allegation in a case that highlights racial tensions in the US.

After more than five hours of arguments during which a prosecutor said Mr Arbery, 25, had been “chased, hunted and ultimately executed”, Glynn County Chief Magistrate Judge Wallace Harrell ruled probable cause existed and the case could go to trial.

Special Agent Richard Dial of the Georgia Bureau of Investigation said William Bryan told his office in an interview in May that Travis McMichael uttered the slur as Mr Arbery lay dying from shotgun wounds on February 23. Mr Bryan and Mr 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—–,” Mr Dial said in testimony.

Travis, left, and Gregory McMichael were each charged over the shooting death of Ahmaud Arbery.

The Arbery case triggered a national outcry after mobile phone video of the shooting was leaked on social media early in May. Thursday’s hearing followed more than a week of protests across the US over the May 25 death in Minneapolis police custody of George Floyd, also a black American.

Four officers have been charged in that case.

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

Mr Dial said the three defendants – Mr Bryan, 50, Mr McMichael, 34, and his father, former police officer Gregory McMichael, 64 – chased Mr Arbery in pick-up trucks and sought to box him in as he was jogging in their neighbourhood.

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

Jason Sheffield, a lawyer for Travis McMichael, pressed Mr Dial on whether Mr Bryan was promised leniency for possible co-operation with prosecutors when he cited the alleged slur and argued his client had acted in self-defence.

Mr Dial said he was unaware of any leniency offer and it was Mr Arbery who was defending himself.

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

Police say Gregory McMichael saw Mr 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, police say.

-AAP