A federal appeals court Wednesday upheld Dylann Roof’s conviction and death sentence for the 2015 racist slayings of nine members of a Black South Carolina congregation, saying the legal record cannot even capture the "full horror" of what he did.

A unanimous three-judge panel of the 4th U.S. Circuit Court of Appeals in Richmond rejected arguments that Roof should have been ruled incompetent to stand trial in the shootings at Mother Emanuel AME Church in Charleston.

In 2017, Roof became the first person in the U.S. sentenced to death for a federal hate crime. Authorities have said Roof opened fire during the closing prayer of a Bible study at the church, raining down dozens of bullets on those assembled. He was 21 at the time.

In this  2017, file photo, Dylann Roof enters the court room at the Charleston County Judicial Center to enter his guilty plea on murder charges in Charleston, S.C. 

In this  2017, file photo, Dylann Roof enters the court room at the Charleston County Judicial Center to enter his guilty plea on murder charges in Charleston, S.C.  (Grace Beahm/The Post And Courier via AP, Pool, File)

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In his appeal, Roof's attorneys argued that he was wrongly allowed to represent himself during sentencing, a critical phase of his trial. Roof successfully prevented jurors from hearing evidence about his mental health, "under the delusion," his attorneys argued, that "he would be rescued from prison by white-nationalists — but only, bizarrely, if he kept his mental-impairments out of the public record."

Roof's lawyers said his convictions and death sentence should be vacated or his case should be sent back to court for a "proper competency evaluation."

The 4th Circuit found that the trial judge did not commit an error when he found Roof was competent to stand trial and issued a scathing rebuke of Roof's crimes.

"Dylann Roof murdered African Americans at their church, during their Bible-study and worship. They had welcomed him. He slaughtered them. He did so with the express intent of terrorizing not just his immediate victims at the historically important Mother Emanuel Church, but as many similar people as would hear of the mass murder," the panel wrote in is ruling.

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"No cold record or careful parsing of statutes and precedents can capture the full horror of what Roof did. His crimes qualify him for the harshest penalty that a just society can impose," the judges wrote.

One of Roof's attorneys, Margaret Alice-Anne Farrand, a deputy federal public defender, declined to comment on the ruling.

All of the judges in the 4th U.S. Circuit Court of Appeals, which covers South Carolina, recused themselves from hearing Roof’s appeal; one of their own, Judge Jay Richardson, prosecuted Roof’s case as an assistant U.S. Attorney. The panel that heard arguments in May and issued the ruling on Wednesday was comprised of judges from several other appellate circuits.

Following his federal trial, Roof was given nine consecutive life sentences after pleading guilty in 2017 to state murder charges, leaving him to await execution in a federal prison and sparing his victims and their families the burden of a second trial.

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Last month, however, Attorney General Merrick Garland issued a moratorium and halted all federal executions while the Justice Department conducts a review of its execution policies and procedures. The review comes after a historic run of capital punishment at the end of the Trump administration, which carried out 13 executions in six months. A federal lawsuit has also been filed over the execution protocols — including the risk of pain and suffering associated with the use of pentobarbital, the drug used for lethal injection.

President Joe Biden as a candidate said he’d work to end federal executions. White House press secretary Jen Psaki said in March that he continues to have "grave concerns" about it.

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Biden has connections to the case. As vice president, Biden attended the funeral for one of those slain, state Sen. Clementa Pinckney, who also pastored the congregation. During his 2020 presidential campaign, Biden frequently referenced the shooting, saying that a visit to Mother Emanuel helped him heal in the aftermath of the death of his son, Beau.

Roof's attorneys could ask the full 4th Circuit to reconsider the panel's ruling. If unsuccessful in his direct appeal, Roof could file what’s known as a 2255 appeal, or a request that the trial court review the constitutionality of his conviction and sentence. He could also petition the U.S. Supreme Court or seek a presidential pardon.