A security guard who was shot on Wednesday in the U.S. Holocaust Memorial Museum died in hospital due to critical wounds, said the museum.

Washington, DC, police officers block the street leading to the main entrance of the Holocaust Museum (C), in Washington, DC, after a shooting. A lone gunman said to have links to white supremacist groups opened fire Wednesday inside the Holocaust Memorial Museum here, fatally wounding a security guard before being shot himself. (Xinhua/AFP Photo)

The museum said in a statement that the slain guard, Stephen Tyrone Johns, died "heroically in the line of duty."

"There are no words to express our grief and shock over these events. He served on the museum's security staff for six years. Our thoughts and prayers go out to Johns' family," said the statement. "We have made the decision to close the museum tomorrow in honor of Johns, and our flags will be flown at half mast in his memory."

FBI officials told reporters that there was no prior warning or threat against the museum, and its National Capital Response Squad and Joint Terrorism Task Force are taking part in the investigation in the case.

According to the capital police department, the shooting was reported to police at 12:52 p.m. local time (1652 GMT) after the gunman walked in the museum and shot a security guard. Another guard returned fire and shot the suspect.

A third person was also injured from broken glasses at the museum.

Police and SWAT officers patrol one of the entrances of the Holocaust Museum in Washington, DC, after a shooting. A lone gunman said to have links to white supremacist groups opened fire Wednesday inside the Holocaust Memorial Museum here, fatally wounding a security guard before being shot himself.(Xinhua/AFP Photo)

U.S. media reported that the gunman had been identified as James von Brunn, a 88-year-old Maryland resident who has links with hate groups and anti-government organizations for a long time.

Reports also said that Von Brunn has a racist, anti-Semitic Website and wrote a book titled "Kill the Best Gentiles," and he was convicted in 1983 of attempting to kidnap members of the Federal Reserve Board.

The museum, which is a popular tourist site in Washington with averagely 1.7 million visitors each year, has a heavy security presence and imposes security check methods.

Washington police, firefighters and other law enforcement officials gather at the scene of a shooting at the U.S. Holocaust Memorial Museum (rear) in Washington June 10, 2009. (Xinhua/Reuters Photo)

White House spokesman Robert Gibbs said that he had informed President Barack Obama of the shooting, and that White House officials are receiving regular updates from the FBI, the Homeland Security Council and the White House.

Editor: Olivia