Washington (CNN) The mayor of Charleston, South Carolina said Sunday that it was "insane" how many guns Americans own and how easy it is to obtain them.

Joseph P. Riley Jr. told CNN's Jake Tapper on "State of the Union" that there were two "pieces of unfinished business" that the U.S. needed to close in order to prevent another attack like the killing of nine South Carolinians by a man, Dylann Roof, believed to have ties to the white supremacist movement.

"It is insane: the number of guns, and the ease of guns in America. It just doesn't fit with the other achievements of this country," Riley said. "It's a small -- really small group, well-funded -- that keeps this issue from being appropriately addressed."

First elected in 1975, Riley also reiterated his support for moving the Confederate flag off the grounds of the state capitol, encouraging state leaders that the flag "needs to go to a museum -- and I think it will."

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