In the years since the terrorist attacks of Sept. 11, 2001, nearly twice as many Americans have been killed by domestic terrorists than by Muslim extremists, according to a new report by New America, a Washington, D.C.-based research center.

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(Left) Charleston, S.C., shooting suspect Dylann Roof, shows Roof posing for a photo while holding a Confederate flag. ( via AP) (Right) Krislynn Rambert, of Charleston, S.C., wears a button in memory of the victims of last week’s mass shooting while waiting on line to enter Sen. Clementa Pinckney’s funeral service, Friday, June 26, 2015, in Charleston, S.C. President Barack Obama will deliver the eulogy at Pinckney’s funeral at a nearby college arena. (AP Photo/David Goldman)

Forty-eight persons have been killed in plots designed by White supremacists, anti-government zealots and other non-Muslim fanatics, compared to 26 killed by jihadists, according to the report’s tally.

The most recent and one of the most devastating homegrown terror acts occurred in Charleston, S.C., where nine members of an African-American church were slain by a self-avowed White supremacist. Other plots often target police officers, members of other minority and religious groups and civilians.

The lethal attack on South Carolina’s Emanuel AME Church was one of 19 carried out by non-jihadists since 9/11, compared to seven by Muslim extremists, according to the count, compiled by David Sterman, a New America program associate, and supervised by Peter Bergen, a terrorism expert.

The new report highlights the gulf between public perception and the reality faced by law enforcement, said John J. Horgan, who studies terrorism at the University of Massachusetts.

“There is an acceptance now of the idea that the threat from jihadi terrorism in the United States has been overblown,” Horgan told The New York Times. “And there’s a belief that the threat of right-wing, anti-government violence has been underestimated.”

A demographic breakdown of the 183 homegrown extremists identified in the period examined showed them to be overwhelmingly U.S.-born citizens of an average age of 34. The majority are male (88.5 percent) and Caucasian (90.7 percent).