Dylann Roof, the man accused of killing nine people including a South Carolina senator at a historical African American church in Charleston last month, was able to purchase the gun he used in the crime due to a background check failure.

FBI chief James Comey said on Friday that 21-year-old Roof should have been stopped from buying a 45-caliber glock weapon in April from a gun store because of a felony charge.

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Comey explained that because the suspect had a pending drug charge, he should never have been allowed to buy the weapon. He described the incident as "a mistake in a matter of heartbreaking importance."

"This rips all of our hearts out " and " we are all sick this happened," he said.

BBC reported that Roof was cleared to purchase the weapon because his drug charge was likely not correctly entered into the background check system or officials may have mishandled the information.

CNN adds that the discrepancy may have been caused by a paper work mix up between the FBI, local police departments and county jurisdictions.

According to the law, gun sellers approve the purchase of weapons after conducting a background check on the buyer.

The FBI has launched an internal inquiry into how the agency utilizes national criminal background checks in gun transactions. The bureau runs background checks for gun dealers and sellers in over 30 states including South Carolina.

The review being conducted by the FBI's inspection division is scheduled to be completed within 30 days.

NBC reported that critics of the country's gun policy have in the past brought up loopholes and problems with the National Instant Criminal Background Check System.

Comey said on Friday that officials had met with the families of the victims to explain how Roof was allowed to buy the weapon used in the massacre.

"Before I wasn't angry, now I'm angry," said Rev. Anthony Thompson, whose wife, Myra, was part of the victims.

Roof's June 17 attack on the Emanuel AME Church has inspired South Carolina lawmakers to remove the Confederate flag from the grounds of the Capitol building. The suspect, who is currently in custody, faces nine counts of murder.

TagsDylann Roof, Charleston shooting, National Instant Criminal Background Check System, James Comey, Emanuel AME Church