The jury has retired at the end of the sentencing phase of convicted murderer Dylann Roof, leaving them to consider whether he will get the death penalty for killing nine people in a South Carolina church.

Roof was unrepentant at his trial today, telling jurors that he felt like he had to carry out the massacre.

Roof, a 22-year-old white supremacist who is representing himself, did not ask the jury to spare his life for the 2015 massacre at Emanuel African Methodist Episcopal Church in Charleston.

"In my confession to the FBI, I told them that I had to do it," Roof said during his short closing argument.

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"I felt like I had to do it when I said that and I still feel that way."

The killer said federal prosecutors who accused him of being filled with hatred did not understand real hate.

He noted it would only take one juror to block the unanimous verdict needed for a death sentence.

"I have a right to ask you to give me a life sentence, but I'm not sure what good that will do anyone," Roof said.

The same jury that last month found Roof guilty of 33 charges, including hate crimes resulting in death, now will weigh whether he should be sentenced to death or sent to prison for life.

A prosecutor argued Roof deserved to die because the shooting was calculated and intended to incite racial violence.

Roof sat for 40 minutes with parishioners gathered for a Bible study meeting on June 17, 2015, before opening fire as they closed their eyes to pray, Assistant US Attorney Jay Richardson said.

"He'd come with a hateful heart and a Glock 45," the prosecutor said during his two-hour final argument. "This was cold and calculated, planned for months, researched for years."

Roof pulled the trigger 75 times as he walked around the room, methodically executing the churchgoers, Richardson said.

Roof has shown no remorse, Richardson said.

"What's wrong here is the calculated racism, the choice to target a church, particularly the people in a church," Richardson said. "What's wrong here is precisely why this is a case that justifies the death penalty."

- Reuters, AAP

The Emanuel AME Church after a memorial for the nine people killed. Photo / AP file
The Emanuel AME Church after a memorial for the nine people killed. Photo / AP file