WASHINGTON -- The gunman charged in the Charleston church massacre should not been allowed to purchase the weapon used in the attack, FBI Director James Comey said Friday as he outlined a series of "heartbreaking" missed opportunities and inaccurate paperwork that allowed the transaction to take place.
"We are all sick that this has happened," Comey told reporters in an unusual, hastily-scheduled meeting at FBI headquarters. "We wish we could turn back time, because from this vantage point, everything seems obvious. But we cannot."
The problems stemmed from an arrest of Dylann Roof in South Carolina weeks before the shooting. During that arrest, police say he admitted to possessing illegal drugs.
CBS News' Paula Reid reports that federal law bans the sale of a firearm to "an unlawful user of or addicted to any controlled substance."
Roof was arrested in March for possession of Suboxone, a Schedule III prescription drug used to treat addiction to opioids. According to the police report, he had admitted using it. Even if he hadn't been convicted of the crime, the FBI says the admission of drug use should have been enough to trip the background check.
But, Comey said, the FBI background check examiner who evaluated Roof's request to buy a gun never saw the arrest report because the wrong arresting agency was listed on the list rap sheet that she reviewed.
"If she had seen that police report," Comey said, "that purchase would have been denied."
The request was on hold for three business days as the FBI examiner sought information about whether it should be approved or rejected. Once that window closed, the firearms dealer used its legal discretion to allow the sale to be completed.
Comey said he learned about the problem on Thursday night and that FBI officials planned to meet Friday with relatives of the nine victims of last month's church shooting in Charleston. He said he had also directed an internal 30-day review into how the FBI uses criminal background checks in gun transactions.
The problem unfolded like this:
Roof went to buy the .45-caliber pistol on April 11 from a licensed firearms dealer, Shooter's Choice, in West Columbia, South Carolina.
The background check examiner assigned to Roof's case identified an arrest on a drug charge. But the arresting agency was listed, for reasons Comey said were unclear, was the Lexington County sheriff's office. The actual arresting agency was the Columbia police department. Had she looked there, she would have seen the arrest report in which Roof admitted having the drug Suboxone, which is used to treat opiate addiction.
The FBI's confusion was further compounded by the examiner's list of police agencies in South Carolina. That list, or contact sheet, placed Columbia in Richland County - where most of the city is located - but not in Lexington County. She selected what she thought was the most reasonable alternative - West Columbia, where the gun shop was located - but the police department there also said it had no record of Roof's arrest. Before she could track down the police report, the three days expired and the gun was sold.
Comey's announcement came within hours of the Confederate flag's removal from the South Carolina Statehouse. Families of the victims attended the ceremony.
Last month, a law enforcement source told CBS News' Pat Milton that a .45 caliber gun was found in the car when Roof was arrested during a traffic stop the day after the shooting. Roof purchased the .45 caliber pistol with $400 his father gave him for his birthday, sources said.
Federal authorities have not said whether they will pursue hate crime charges against Roof.
Roof is next expected in court in October on murder charges.