Dylann Roof, who was charged over the massacre of nine black parishioners at a church in Charleston last June, was assaulted by a fellow inmate yesterday.

Roof, 22, was left with bruising on his face and back after the assault in the shower by Dwayne Stafford, 26. The attack was "unprovoked" according to a police report.

Roof was examined by jail medical personnel and then returned to his cell, according to Charleston County Sheriff's Eric Watson.

It was earlier reported that Stafford would be charged with third-degree assault but Charleston County Sheriff Al Cannon later said that Roof and his attorneys do not want to press charges.

Cannon added that officials are investigating how Stafford managed to make his way through a cell door to reach Roof. The two detention officers assigned to the unit are being interviewed, and officials also are investigating the possibility of an electronic malfunction, Cannon said.

Stafford is awaiting trial on first-degree assault and strong armed robbery charges.

Roof has been housed at the Charleston County detention centre since being returned from North Carolina a day after the killings on 17 June 2015 of nine parishioners during a Bible study at Emanuel AME Church.

Prosecutors have said that Roof, who faces the death penalty in upcoming trials in both federal and state courts, was trying to make his way to Nashville, Tennessee, after the shootings.

Prosecutors have also said that Roof discussed starting a race war and posed with the controversial Confederate battle flag before the killings.

Roof is due to stand federal trial in November, and faces the prospect of a death penalty sentence in state court where he is charged with nine counts of murder.

Defense attorneys have said in both state and federal courts that Roof is willing to plead guilty and serve a life term in prison instead of the death penalty, which they have argued is unconstitutional.