A lawsuit has been filed against the Federal Bureau of Investigation (FBI) by the families of the victims and survivors of last year's shooting at the Emanuel AME Church in Charleston, South Carolina over the agency's alleged failure to stop the suspect from buying a gun.

Nine people were killed including state Senator Clementa Pinckney when gunman Dylann Roof, 22, a white supremacist, opened fire inside the church on June 17, 2015.

Roof was subsequently arrested and charged with nine counts of murder. He faces the death penalty if convicted, according to The Independent.

In the lawsuit, the FBI is accused of failing to do a thorough background check on Roof when he bought the gun last year.

"If the gun sale was denied as required, it would have prevented the foreseeable harm to those people," said the families in the lawsuit.

Lawyer Andrew Savage, who represents three survivors and relatives of five victims, said, "The victims and families hope that by bringing these actions, they can shine a very bright light on these shortcomings and prevent other individuals, families and communities from dealing with unfathomable and preventable loss and injury," the Washington Post reports.

Roof should not have been allowed to buy a gun because of his previous admission for using illegal drug.

A West Columbia gun store owner sold Roof a .45 calibre Glock that authorities said was the firearm used by Roof in killing nine people in the church, according to The Post & Courier.

"The victims' civil suit against the FBI seeks to hold the government accountable to the law and demonstrate it's not above the law," said lawyer Mullins McLeod Jr., who represents several victims' relatives.

The relatives and survivors filed the lawsuit based on the Federal Tort Claims Act, which allows citizens to sue the federal government.

After the shooting, FBI Director James Comey said in July 2015 that Roof should not have been allowed to buy a gun.

"I'm here today to talk to you about a mistake, in a matter of heartbreaking importance to all of us. Dylann Roof, the alleged killer of so many innocent people at the Emanuel AME church, should not have been allowed to purchase the gun he allegedly used that evening," said Comey.