(AP) — A grand jury returned an indictment Wednesday against Payton Gendron, the white 18-year-old accused of fatally shooting 10 Black people in a racist attack at a Buffalo supermarket, according to the district attorney’s office.

Gendron, who has been in custody since the May 14 shooting, is scheduled to be arraigned Thursday in Erie County Court.

The charge or charges will not be disclosed until his court appearance, the Erie County District Attorney’s office said.

Gendron had previously been charged with first-degree murder in the shooting, which also injured three people. He has pleaded not guilty. Prosecutors told a judge May 20 the grand jury had voted to indict Gendron but was continuing its investigation. It was unclear whether the finalized indictment contains any new allegations against Gendron.

Federal authorities also are investigating the possibility of hate crime charges against Gendron, who apparently detailed his plans and his racist motivation in hundreds of pages of writings he posted online shortly before the shooting. The attack was livestreamed from a helmet-mounted camera.

Gendron drove about three hours from his home in Conklin, New York, intending to kill as many Black people as possible, investigators have said.

His attorney, Brian Parker, said he had not seen the indictment and could not comment, adding that prosecution and defense attorneys have been barred by a judge from discussing the case publicly.