An elderly gunman, said by authorities to have a violent and virulently anti-Semitic past, stepped inside the crowded U.S. Holocaust Memorial Museum on Wednesday, opened fire with a rifle and fatally wounded a security guard before being shot by other officers.

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 Von Brunn, 88, a white supremacist, was under investigation in the shooting, and a second official said the elderly man’s car was found near the museum and tested for explosives. 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. In an e-mail, director Sara Bloomfield said he “died heroically in the line of duty.”

Von Brunn has a racist, anti-Semitic Web site and wrote a book titled “Kill the Best Gentiles.”

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.”

“At Auschwitz the ‘Holocaust’ myth became Reality, and Germany, cultural gem of the West, became a pariah among world nations,” it says.

The museum, which opened in 1993 and has drawn nearly 30 million visitors, houses exhibits and records relating to the Holocaust of more than a half century ago in which more than six million Jews died at the hands of Nazis. Its Web site says the museum “teaches millions of people each year about the dangers of unchecked hatred and the need to prevent genocide.”

The museum was crowded with school children and other tourists at the time of the attack, but they all escaped injury in the outburst of violence.

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, she recalled, 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.”

The attack was the third in a recent wave of unsettling shootings 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 was 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.

At the White House a few blocks away from the museum, press secretary Robert Gibbs said he informed President Barack Obama of the events and the chief executive was “obviously saddened by what has happened.”

Only last week, Obama visited the site of a German concentration camp at Buchenwald in Germany where he noted, “There are those who insist the Holocaust never happened.” He added, “This place is the ultimate rebuke to such thoughts, a reminder of our duty to confront those who would tell lies about our history.”