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(CNN) Dylann Roof, the man who allegedly killed nine people in a Charleston church last month, should not have been able to buy a gun used in the slaughter, the FBI has now determined, contradicting earlier assertions that the background check was done properly, a law enforcement official tells CNN and FBI's director told reporters in Washington.

FBI Director James Comey told reporters Friday "this rips all of our hearts out" and "we are all sick this happened." He said he concluded the mistake had been made Thursday night after reviewing the latest information.

Photos: Manifesto photos feature Dylann Roof Photos: Manifesto photos feature Dylann Roof A website featuring a racist manifesto and 60 photos has become part of the investigation into Dylann Roof , who has been charged in the slaying of nine people at Charleston's Emanuel African Methodist Episcopal Church on June 17. Hide Caption 1 of 5 Photos: Manifesto photos feature Dylann Roof Three photos show Roof posing with a pistol. One closeup shows a gun that can be identified as a .45-caliber Glock -- the model of gun investigators say was used in the church shooting. Those photos were taken in April, after his 21st birthday, when his family said he purchased a .45-caliber gun. Hide Caption 2 of 5 Photos: Manifesto photos feature Dylann Roof It's not clear who took any of the 60 photos, which were shot between August 3, 2014, and June 17, with the majority shot in March and April. Roof appears alone in many of them, never smiling. The other pictures show objects or landscapes and no other people. Hide Caption 3 of 5 Photos: Manifesto photos feature Dylann Roof Photos taken May 11 show Roof burning and spitting on an American flag. Another May 11 photo shows him holding a small Confederate flag. Hide Caption 4 of 5 Photos: Manifesto photos feature Dylann Roof Motive has become the biggest question as state and federal investigators work on the case -- and statements and photos on the website match what investigators have determined so far. Hide Caption 5 of 5

Within days after the shooting, agents on the ground knew something was amiss and suspected that Roof's arrest record should have prohibited the gun purchase, according to law enforcement officials.

Officials began a review, as is common after major shootings. About a week after the shooting, examiners officially denied the Roof application.

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