Dylann Roof has been sentenced to death for killing nine black church members during Bible study in a racially motivated attack in South Carolina.

He became the first person to face execution for federal hate crime convictions.

A jury deliberated his sentence for about three hours, capping a trial in which Roof did not fight for his life or show any remorse.

At the beginning of the trial, he addressed jurors directly, insisting that he was not mentally ill, but he never asked them for forgiveness or mercy, or explained the crime.

He threw away one last chance to plead for his life on Tuesday, telling jurors: "I still feel like I had to do it."

Every juror looked directly at Roof as he spoke for about five minutes.

A few nodded as he reminded them that they said during jury selection they could fairly weigh the factors of his case.

Only one of them, he noted, had to disagree to spare his life.

"I have the right to ask you to give me a life sentence, but I'm not sure what good it would do anyway," he said.

When the verdict was read, he stood stoic and showed no emotion. He will be formally sentenced on Wednesday.

Roof told FBI agents when they arrested him a day after the June 17 2015 killings that he wanted the shootings to bring back segregation or perhaps start a race war.

Instead, the killings had a unifying effect, as South Carolina removed the Confederate flag from its Statehouse for the first time in more than 50 years and other states followed suit, taking down Confederate banners and monuments.

Roof had posed with the flag in photos.

The attacker specifically picked out Emanuel AME Church, the South's oldest black church, to carry out the cold, calculated slaughter, Assistant US Attorney Jay Richardson said.

The 12 people Roof targeted opened the door for a stranger with a smile, he said. Three people survived the attack.

"They welcomed a 13th person that night ... with a kind word, a Bible, a handout and a chair," Mr Richardson said during his closing argument.

"He had come with a hateful heart and a Glock .45."

The gunman sat with the Bible study group for about 45 minutes.

During the final prayer - when everyone's eyes were closed - he started firing.

He stood over some of the victims, shooting them again as they lay on the floor, Mr Richardson said.

The prosecutor reminded jurors about each one of the victims and the bloody scene that Roof left in the church's lower level.

The jury convicted him last month of all 33 federal charges he faced, including hate crimes.

Roof did not explain his actions to jurors, saying only that "anyone who hates anything in their mind has a good reason for it".

Nearly two dozen friends and relatives of the victims gave evidence during the sentencing phase of the trial.

They shared cherished memories and talked about a future without a mother, father, sister or brother.

They shed tears and their voices shook, but none of them said whether Roof should face the death penalty.

Mr Richardson recalled Jennifer Pinckney's remarks about her husband, Clementa, who was remembered for singing goofy songs and watching cartoons with their young daughters in his spare time.

After more than two hours of discussions, jurors re-watched a speech by Mr Pinckney, the church pastor and a state senator.

In it, Mr Pinckney talks about the history of Emanuel and its mission.

Roof acted as his own lawyer and did not question any witnesses or put up any evidence.

The last person sent to federal death row was Boston Marathon bomber Dzhokhar Tsarnaev in 2015.

Malcolm Graham, whose sister Cynthia Hurd was killed, said he thought the jury made the right decision.

"There is no room in America's smallest jail cell for hatred, racism and discrimination," he said from his home in Charlotte, North Carolina.

"The journey for me and my family today has come to an end."

In a statement after Roof was sentenced to death, his relatives said they would "struggle as long as we live" to understand why he killed the parishioners.

The relatives, who have not returned to court since the start of his trial, "express the grief we feel for the victims of his crimes, and our sympathy to the many families he has hurt".

In another statement, Roof's legal advisers said they were sorry that "despite our best efforts, the legal proceedings have shed so little light on the reasons for this tragedy" - a veiled referenced to the mental issues they wanted to present during sentencing.

Roof acted as his own lawyer and said he was not mentally ill.

Father John Parker, an Eastern Orthodox minister described as Roof's spiritual adviser, said in a statement he condemned "Dylann's unspeakable crimes" and prays for the victims.