The Department of Justice notified a federal judge Tuesday that it will seek the death penalty against the man accused of killing nine people last year in a Charleston, South Carolina, church.
"The nature of the alleged crime and the resulting harm compelled this decision," said Attorney General Loretta Lynch.
Roof, 22, is already charged with murder in state court for the shooting rampage at the historically black Emanuel AME Church, and state prosecutors announced earlier that they would seek the death penalty.
A South Carolina judge has ordered Roof to stand trial on the state charges in January.
Federal prosecutors will almost certainly wait until that case has concluded before deciding whether to seek a trial in federal court.
Justice Department officials, however, filed their own charges, because they believed the severity of the crime warranted a strong response
In listing the reasons for seeking the death penalty, federal prosecutors said Roof "targeted men and women participating in a Bible study group" at the church "in order to magnify the societal impact" of his shootings.
His acts were also racially motivated, the prosecutor said. "Dylann Storm Roof has expressed hatred and contempt towards African Americans, as well as other groups, and his animosity toward African Americans played a role in the murders."
What's more, they said, he has demonstrated a lack of remorse.
Roof has pleaded not guilty to the charges. No trial date has been set in federal court.