An elderly man identified by authorities as a white supremacist has been charged with murder in the shooting of a security guard at the Holocaust museum in Washington, D.C.

U.S. Holocaust Memorial Museum security officer Stephen Tyrone Johns is pictured in this undated photograph. He was shot and killed at the museum on Wednesday afternoon. (U.S. Holocaust Memorial Museum/Reuters)

James Wenneker von Brunn, 88, was charged with murder in the killing of Stephen Tyrone Johns, said Cathy Lanier, chief of Washington's city police. Von Brunn has also been charged with discharging a firearm in a federal facility, she told reporters at a news conference Thursday.

Johns, a 39-year-old security guard who worked for six years at the United States Holocaust Memorial Museum, was killed Wednesday afternoon after a man walked into the facility carrying a rifle and immediately opened fire.

Johns held the door open for his assailant before being shot, Lanier said.

Two other security guards at the museum fired at the assailant, who is now in hospital in critical condition, authorities said.

"This is a tragic reminder that local law enforcement and private security play a critical role in the safety of our nation," Lanier said. "And the heroism displayed yesterday by the special police officers at the museum should not go unnoticed by the rest of the nation."

The museum was closed and flags were at half-mast Thursday in honour of Johns, who had an 11-year-old son.

Washington Mayor Adrian Fenty said quick work by law enforcement "literally saved the lives of countless people."

The museum, located just off the National Mall near the Washington Monument, is a popular tourist attraction that draws about 1.7 million visitors each year.

Potential hate crime charges: FBI

Authorities have no information indicating that the assailant had any assistants or accomplices, Joseph Persichini, assistant director of the District FBI field office, said Thursday.

"We are continuing and working with the Department of Justice and the U.S. attorney's office, looking at potential civil rights or hate crimes that he can also be charged with at a later date," Joseph said.

"Again, we have so much to do — there's a lot of work and a lot of data and materials to review."

James von Brunn, seen in a photo from his website, is charged with murder in the case. (HolyWesternEmpire.org/Reuters)

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

The U.S. 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.

Grim history

Von Brunn has described himself as a victim of a court system controlled by Jews and blacks.

He has a racist, anti-Semitic website and wrote a book titled Kill the Best Gentiles, alleging a Jewish "conspiracy to destroy the white gene pool," the Associated Press reported.

In 1983, he was convicted of attempting to kidnap members of the Federal Reserve Board and served more than six years in prison. He was arrested two years earlier outside the room where the board was meeting, carrying a revolver, knife and sawed-off shotgun.

At the time, police said von Brunn wanted to take the members hostage because of high interest rates and the nation's economic difficulties.

Writings attributed to von Brunn on the internet say the Holocaust was a hoax and decry a Jewish conspiracy to "destroy the white gene pool."

With files from The Associated Press