NEW YORK, United States (AP) — The white man charged with murdering 10 Black people at a supermarket in Buffalo appeared briefly in court Thursday after a grand jury indicted him on a first-degree murder charge.

Assistant district attorney Gary Hackbush said the indictment of Payton Gendron, 18, was handed up Wednesday.

Gendron, wearing an orange jail uniform and a mask, was silent throughout the proceeding attended by some relatives of the victims.

He is being held in jail without bail.

In New York, prosecutors can charge a defendant with first-degree murder only under special circumstances, including when multiple people are killed in a single incident, like in the Buffalo shooting. The single count against Gendron covers all 10 deaths at the supermarket.

Thirteen people in all were shot Saturday at the Tops Friendly Market in a predominantly Black neighborhood of Buffalo. Authorities are continuing to investigate the possibility of hate crime and terrorism charges.

Gendron, 18, livestreamed the attack from a helmet camera before surrendering to police outside the grocery store. Shortly before the attack, he posted hundreds of pages of writings to online discussion groups where he detailed his plans for the assault and his racist motivation.

Investigators have been examining those documents, which included a private diary he kept on the chat platform Discord.

At his initial court appearance last week, Gendron’s court-appointed lawyer entered a plea of “not guilty” on his behalf. He is due back in court June 9.

All but two of the 13 of the people shot during the attack were Black. Gendron’s online writings said he planned the assault after becoming infatuated with white supremacist ideology he encountered online.

The diary said Gendron planned his attack in secret, with no outside help, but Discord confirmed Wednesday that an invitation to access his private writings was sent to a small group of people about 30 minutes before the assault began.

Some of them accepted the invitation. It was unclear how many read what he had written or logged on to view the assault live. It also wasn’t clear whether anyone tried to alert law enforcement.

Buffalo Police Commissioner Joseph Gramaglia has said investigators were working to obtain, verify and review Gendron’s online postings.