An 88-year-old gunman with a violent and virulently anti-Semitic past opened fire with a rifle inside the crowded U.S. Holocaust Memorial Museum on Wednesday, fatally wounding a security guard before being shot himself by other officers, authorities said.

The assailant was hospitalized in critical condition, leaving behind a sprawling investigation by federal and local law enforcement and expressions of shock from the Israeli government and a prominent Muslim organization.

Washington Police Chief Cathy Lanier said the gunman was "engaged by security guards immediately after entering the door" with a rifle. "The second he stepped into the building he began firing."

Law enforcement officials said James W. von Brunn, a white supremacist, was under investigation in the shooting and that his car was found near the museum and tested for explosives. The weapon was a .22-caliber rifle, they added. They spoke on condition of anonymity, saying they were not authorized to discuss the investigation just beginning.

Museum officials identified the dead guard as Stephen T. Johns, a six-year veteran of the facility. Director Sara Bloomfield said he "died heroically in the line of duty," AP reported.