The monument, known as the Georgia Guidestones, which was erected about nine miles north of Elberton, Ga., had four granite slabs attached to a central pillar, with a headstone on top. But around 4 a.m. Wednesday, an explosive device detonated, destroying “a large portion of the structure,” the Georgia Bureau of Investigation said in a statement. He is investigating the explosion along with the Elbert County Sheriff’s Office. On Wednesday afternoon, the Georgia Bureau of Investigation released surveillance video that captured the explosion, which threw pieces of the monument out and sent dust into the air. A short time later, a car is seen on the footage leaving the scene, according to the agency. He said that “for security reasons”, the remaining pillars had been “completely demolished”. For more than four decades, the Guidestones have towered over a field, fascinating and confounding many visitors. It is unclear why the 19-foot-long granite slabs were there or what they meant, and only one man claimed to know the identity of the benefactor who paid for them. The man, Wyatt Martin, claimed another man named RC Christian had paid for the granite slabs in 1979 after visiting the East Georgia town. “I made an oath to this man and I can’t break it,” Mr. Martin, who helped arrange the memorial, told The New York Times in 2013. He added, “No one will ever know.” The granite slabs, the department says on its website, display “a 10-part message supporting the preservation of humanity and future generations in 12 languages.” It also serves as an astronomical calendar: Every day at noon the sun shines through a narrow hole in the structure, illuminating the day’s date. Despite the mysterious aura of the Guidestones, some local residents said they don’t care much for them. Some conspiracy theorists have argued that the edicts of the stones — which include a call to “unify humanity with a living new language” and a recommendation to keep the planet’s population below 500 million — represent an elite plan to depopulate the planet . “They built this monument calling for the forced desolation of the planet,” Alex Jones, the far-right broadcaster and conspiracy theorist, said in a 2020 video. In a post on Twitter, Georgia Republican gubernatorial candidate Candace Taylor appeared to welcome the partial destruction of the monument, which she described as “Satanic Guides.” Mart Clamp, a local businessman who helped his father carve the Guidestones when they were first erected, said he was “hurt” at the damage caused by the blast. “People have always made up a crazy story about them,” he said of those who promoted conspiracy theories about the plaques. “It’s unfortunate that we live in a society that thinks it’s acceptable to tear down things you disagree with,” Mr Clamp added. “Right now I have no words.” He said many local businesses in the area, including his own, which carves stones, had donated their time and resources to restore the structure. “If we’re allowed,” added Mr. Clamp, “we’ll rebuild them.” Eduardo Medina contributed reporting.