An 88-year-old white supremacist will be charged with the murder of a security guard at the Holocaust museum in Washington, authorities said Thursday.

Police will file formal federal charges against James Von Brunn in the shooting death of guard Stephen T. Johns, Washington D.C. Mayor Adrian Fenty told reporters.

Von Brunn will be charged with murder and killing in the course of possessing a firearm at a federal facility, both capital offenses. Hate-crime charges also are possible at a later date, authorities said.

"We know what Mr. Von Brunn did yesterday at the Holocaust museum. Now it's our responsibility to determine why he did it," said Joseph Persichini, assistant director of the Washington FBI field office. "We have to ask ourselves did all these years of public display of hatred impact his actions."

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Johns, 39, was shot by Von Brunn after opening the door to let him into the U.S. Holocaust Memorial Museum, District Police Chief Cathy Lanier said at a news conference. Johns died later at the hospital.

Von Brunn, who once tried to kidnap members of the Federal Reserve, then exchanged fire with guards who shot and critically injured him, stopping him from entering the museum and hurting anyone else, Lanier said.

Police have executed search warrants on Von Brunn's home and vehicle and are searching his computer, records and other data, authorities said Thursday. They're also developing a timeline of events.

The museum was closed and flags flew at half-staff Thursday in honor of Johns. Fenty said quick work by law enforcement "literally saved the lives of countless people."

Johns, who is black, "died heroically in the line of duty," museum director Sara Bloomfield said.

Johns was being treated at a Washington hospital. A self-described artist, advertising man and author living in Annapolis, Md., Von Brunn wrote an anti-Semitic treatise, "Kill the Best Gentiles," decried "the browning of America" and claimed to expose a Jewish conspiracy "to destroy the White gene-pool."

He also wrote of a lifetime of seething anger.

"It's better to be strong than right," he said in one of his dark screeds online, "unless you like dying. Crowds hate good guys."

The Homeland Security Department called the shooting a criminal incident and said it does not appear to have a connection to terrorism, according to a joint Homeland Security and FBI assessment issued Wednesday. The assessment, obtained Thursday by The Associated Press, said Von Brunn is associated with right-wing extremism.

When Von Brunn was captured after the shooting, he had a list he had made of lawmakers on Capitol Hill, according to a law enforcement official. The purpose of the list was not immediately clear, said the official, who requested anonymity because he was not authorized to speak publicly.

Investigators are trying to determine how Von Brunn acquired the .22-caliber rifle used in the attack, said two other law enforcement officials, also speaking on condition of anonymity.

Israeli officials and U.S. Muslim and Hispanic groups all expressed shock at the attack, which unfolded in a public space filled with records, photographs and exhibits standing as stark testament to the Nazis' killing more than 6 million Jews in the Holocaust of more than a half-century ago.

The museum was crowded with schoolchildren and other tourists, but all escaped injury.

Ashley Camp, 14, of Forsyth, Ill., on a field trip with more than 40 other students, said she heard two or three gunshots. Soon after, a security guard ordered the group to run to the exit.

"We had to sprint as fast as we could out the door," she said. "I thought it was the movie (part of a museum exhibit), but then everyone started screaming and running."

Law enforcement officials said Von Brunn's car was found near the museum and was tested for explosives. They spoke on condition of anonymity, saying they were not authorized to discuss the investigation.

Von Brunn was sentenced in 1983 for attempted armed kidnapping and other charges in his 1981 bid to seize Fed board members. A guard captured him outside the room where the board was meeting. He had a revolver, sawed-off shotgun and knife in a bag with him. He served more than six years in prison.

"The subject resides in my memory like old road-kill," he wrote of the capture. "What could have been a slam-bang victory turned into ignoble failure. Recalling all of this presents an onerous task. I am getting near the end of the diving board."

Von Brunn is a native of St. Louis, a World War II veteran who served in the Navy for about 14 years, worked in advertising in New York City and moved to Maryland's Eastern Shore in the late 1960s, where he stayed in advertising and tried to make a mark as an artist. He was living in New Hampshire the year of his arrest at the Fed headquarters.

Public records show that in 2004 and 2005 he lived briefly in Hayden, Idaho, which for years was home to the Aryan Nations, a racist group run by neo-Nazi Richard Butler.

Civil rights groups were familiar with his virulent history.

"We've been tracking this guy for decades," said Heidi Beirich, director of research for the Southern Poverty Law Center's Intelligence Project, which tracks hate crimes. "He thinks the Jews control the Federal Reserve, the banking system, that basically all Jews are evil," she said. "He's an extreme anti-Semite."

His Internet writings say the Holocaust was a hoax. "At Auschwitz the 'Holocaust' myth became Reality, and Germany, cultural gem of the West, became a pariah among world nations," he wrote.

The attack is "further proof that anti-Semitism and Holocaust denial have not passed from the world," said Israel's information and Diaspora minister, Yuli Edelstein.

"It's the first domestic terrorist of this age that we've seen," Beirich said. "It just shows you it doesn't matter what age you are — you can be driven to violence from these belief systems."

The attack was the third unsettling shooting that appeared to have political underpinnings.

A 23-year-old Army private, William Andrew Long, was shot and killed outside a recruiting office this month in Arkansas and a fellow soldier wounded. The suspect, a Muslim convert, has said he considers the killing justified because of the U.S. military presence in the Middle East.

Late last month, abortion provider Dr. George Tiller was shot to death in his church. The man accused of killing him is a longtime vocal opponent of abortion.

At the White House, just blocks away from the museum, President Barack Obama said: "This outrageous act reminds us that we must remain vigilant against anti-Semitism and prejudice in all its forms. No American institution is more important to this effort than the Holocaust Museum, and no act of violence will diminish our determination to honor those who were lost by building a more peaceful and tolerant world."

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The Associated Press contributed to this report.