Dylann Roof, who allegedly shot and killed nine people at the Emanuel African Methodist Episcopal Church in Charleston, South Carolina in June 2015, visited Charleston at least six times and drove by the church several times before the massacre, according to an FBI agent.

Joseph Hamski, the lead federal agent on Roof's case, told jurors at Roof's federal death penalty trial on Tuesday that GPS readings from Roof's car showed how the self-described white supremacist's apparent scouting trips also included stops at historic plantations and Fort Moultrie, the US arrival point for thousands of African slaves in the 18th and 19th centuries. Roof always travelled alone, Hamski said.

In February 2015, Roof called the church from a landline at his mother's home near Columbia, Hamski said.

Roof, 22, has confessed he targeted the church. Law enforcement officers who took the stand on the fifth day of testimony in Charleston detailed their findings of Roof's racist ideology and a timeline of the months he appeared to spend planning the mass shooting.

Photos found at his mother's home showed Roof pointing his gun at a camera and sitting on a bed wearing a pointed white hood, investigators said, referring to a garment traditionally worn by members of the Ku Klux Klan hate group.

Jurors saw chilling video Roof made of himself taking target practice with a laser sight mounted on a pistol in his mother's backyard and surveillance footage from stores where he bought hundreds of rounds of ammunition.

"Did your investigation reveal that Mr Roof was a member of any organisation?" defence lawyer David Bruck asked Hamski on cross examination.

"No," said the agent, adding that investigators determined Roof acted alone in the shooting.

Earlier on Tuesday, US District Judge Richard Gergel said he would not allow the defence to call witnesses to testify about Roof's state of mind and personal characteristics until the penalty phase of the trial.

The defence has not disputed Roof's guilt on federal charges of hate crimes resulting in death, obstruction of religion and firearms violations but hope jurors will spare him from execution.

Roof is not asserting an insanity defence and was found competent to stand trial, Gergel noted in a written order on Monday.

Prosecutors said they expect to finish their case on Wednesday with testimony from Polly Sheppard, who was at the church but not killed because Roof said he wanted her tell what he had done.

Additional reporting by Reuters.