WASHINGTON (AFP) - The three men arrested after the killing of Ahmaud Arbery, a young black jogger in the southern United States, were formally indicted on murder charges by a grand jury on Wednesday (June 24).

Arbery, 25, was shot dead on Feb 23 while running in a residential area of Brunswick, Georgia, which has a long history of segregation.

For more than two months, local police did not make any arrests. It was only when video of the killing went viral on social media at the beginning of May that the investigation began in earnest.

Retired police officer Gregory McMichael, 64, and his son Travis, 34, who were visible on the video, were arrested on May 7.

The man who filmed the killing, William Bryan, 50, was arrested two weeks later.

The indictment was formalised on Wednesday by a grand jury, a group of citizens appointed to weigh how valid a charge is ahead of a trial.

Nine counts, including murder, aggravated assault and false imprisonment were laid against the three men.

They "caused his death by unlawfully chasing him... in pickup trucks and shooting him with a shotgun," the document said.

Arbery's name has been chanted for weeks all over the United States during giant demonstrations protesting violence and systemic racism against African Americans.

He joins a list including George Floyd, who suffocated beneath the knee of a white police officer and whose killing on May 25 kicked off the protests; and Breonna Taylor, shot dead as she slept at her home in Louisville, Kentucky on March 13 by police who had apparently burst into the wrong apartment.