Federal prosecutors will seek the death penalty against the gunman who killed 10 Black people in a racist massacre at a Buffalo supermarket in May 2022, according to court papers filed on Friday. It is the first time that President Biden’s administration has sought the death penalty in a new case.

The gunman, Payton Gendron, who committed the attack after posting a hate-filled white supremacist manifesto online, had already been sentenced to life in prison without the chance of parole on state charges last year. He had pleaded guilty to 10 counts of first-degree murder and a single count of domestic terrorism motivated by hate.

The federal government had charged Mr. Gendron, 20, with hate crimes and gun charges that could bring the death penalty. Prosecutors said in the Friday filing in the Western District of New York that the circumstances of the charges were “such that, in the event of a conviction, a sentence of death is justified.” Mr. Gendron, in choosing the location of the shooting did so “in order to maximize the number of Black victims of the offense,” prosecutors wrote.

A spokeswoman for the Justice Department declined to comment on the case.

Outside the federal courthouse in Buffalo on Friday, Mark Talley, the son of one of the victims, Geraldine Talley, said emotions were fraught when prosecutors told the families of the 13 victims, including three who were wounded, about the decision. Mr. Talley, 33, the author of a book about the shooting, said he understood why some would welcome the news. He did not.