Washington, Jul 11 (IANS/EFE): A failure in the federal background check system allowed Dylann Roof to obtain the gun he allegedly used in killing nine black churchgoers last month in South Carolina, FBI Director James Comey said.

"This case rips all of our hearts out, but the thought that an error on our part is connected to a gun this person used to slaughter these people is very painful to us," Comey told reporters on Friday.

"We wish we could turn back time," he added.

When the 21-year-old Roof tried to buy a .45-calibre handgun in West Columbia, South Carolina, on April 11, the FBI examiner reviewing his request saw a narcotics arrest in February by the Lexington county sheriff's department.

Her investigation eventually led to her contacting the police department serving the state capital of Columbia, but since the city is spread over two counties it also has two police departments.

The examiner contacted the West Columbia police department, based in Lexington county, but not the Columbia police department, which is located in Richland county and had possession of a report in which Roof had admitted to possession of a drug.

That admission would have disqualified him from purchasing the weapon.

The shooting occurred around 9 p.m. on June 11, an hour after the white suspect entered the city of Charleston's Emanuel African Methodist Episcopal church during Bible study.

He killed all but three of the 12 people who were in the church with him at the time of the attack.

The tragedy has re-ignited debate in several southern states about the presence of the Confederate battle flag on the grounds of government buildings, since Roof had posed for numerous photos with that flag prior to the killings.

Also known as the "Southern Cross", the flag was adopted as the symbol of the breakaway, pro-slavery confederate states of America and was used in battle from late 1861 until the fall of the confederacy in 1865.

On Friday, that Confederate flag was removed from the grounds of South Carolina's State House in Columbia.

The state legislature had given final approval to a bill to take down the flag on Thursday morning and Governor Nikki Haley signed it into law later that day.