The death sentence has been upheld for the gunman responsible for killing nine African Americans at a Charleston church.

Dylann Roof opened fire at the Emanuel African Methodist Episcopal Church in June 2015 as a Bible study was taking place.

He had been invited to join the Wednesday Bible study by the churchgoers but instead turned the gun on them in what was a racially motivated attack. 

When he was sentenced to death in 2017, he showed no remorse for his actions, telling jurors, "I still feel like I had to it."

Now a federal appeals court has rejected a request to commute his death sentence. 

The written judgment speaks of the coldness with which Roof murdered the victims. 

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"Dylann Roof murdered African Americans at their church, during their Bible-study and worship. They had welcomed him. He slaughtered them," it said.

"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.

"He used the internet to plan his attack and, using his crimes as a catalyst, intended to foment racial division and strife across America.

"He wanted the widest possible publicity for his atrocities, and, to that end, he purposefully left one person alive in the church 'to tell the story.' When apprehended, he frankly confessed, with barely a hint of remorse." 

The judgment goes on to state that the death sentence is justified in his case.

"No cold record or careful parsing of statutes and precedents can capture the full horror of what Roof did," the court said.

"His crimes qualify him for the harshest penalty that a just society can impose. We have reached that conclusion not as a product of emotion but through a thorough analytical process."