U.S. Secretary of State Hillary Clinton on Thursday described a shooting at Washington D.C.'s Holocaust Museum as a “terrible tragedy,” as museum staff said the building would close for a day to honor a security guard killed in the shooting a day earlier. “It was a terrible and the kind of hatred that the killer evidenced over many years toward different groups within our society is deplorable,” Clinton said in response to a reporter's question. “I hope that all of America will stand united against that kind of terrible action on the part of anyone who harbors those feelings and attitudes,” she said. Clinton's comments came as more details emerged about the incident and the shooter – James Von Brunn, an aging white supremacist and anti-Semite. Washington D.C. Chief of Police Cathy Lanier said Von Brunn appeared to be acting alone when he entered the museum Wednesday afternoon. She also said that security guard Stephen Jones held open the door of the museum for Von Brunn, who is believed to be 88 or 89 years old. Von Brunn immediately opened fire, shooting Jones before himself being hit by gunfire from another security guard. Both Von Brunn and Jones were taken to a local hospital, where Jones died on Wednesday afternoon. Police said Thursday that Von Brunn would be charged with murder. He remains in hospital in critical condition.