BUFFALO, N.Y. -- A day after the white supremacist gunman who killed 10 Black people at a Buffalo supermarket was sentenced to life in state prison, attention turned Thursday to federal hate crime charges and the potential for the death penalty.

During a procedural hearing, U.S. marshals were given temporary custody of Payton Gendron, 19, while he awaits trial on a 27-count federal indictment. Gendron spoke only to agree to the transfer.

He was sentenced to multiple life sentences with no chance at parole Wednesday after pleading guilty to state charges of murder and domestic terrorism motivated by hate. His attorneys say he would also plead guilty in the separate federal case to avoid execution.

U.S. Attorney General Merrick Garland has not ruled out seeking the death penalty against the gunman, who was 18 when he opened fire in a predominantly Black neighbourhood 200 miles from his mostly white hometown of Conklin. Assistant U.S. Attorney Joseph Tripi indicated discussions are ongoing.

New York does not have capital punishment -- life without parole is the maximum sentence -- but the death sentence is still an option in federal court, where Gendron is charged with hate crimes resulting in death and discharging a firearm to commit murder. The latter charge is a capital offence.

A trial could be scheduled for July if the case is not resolved before then, U.S. Magistrate Judge H. Kenneth Schroeder said.

At Wednesday's sentencing, Gendron apologized for the attack that he planned for months and live-streamed over the internet using a GoPro video camera.

"I cannot express how much I regret all the decisions I made leading up to my actions on May 14," Gendron said after listening to relatives of his victims express rage and sorrow in a series of victim impact statements. "I did a terrible thing that day. I shot and killed people because they were Black."

According to the federal complaint, the semi-automatic rifle Gendron used was marked with racial slurs and various phrases, including "The Great Replacement," a reference to a conspiracy theory that says there's a plot to diminish the influence of white people.

The complaint also references detailed written plans by Gendron, including that he researched the zip code with the highest percentage of Black people reachable from his home and chose the Tops store for its concentration of Black shoppers and employees.