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A security guard at the U.S. Holocaust Memorial Museum who was fatally shot was described as a warm man with a wonderful smile who acted courageously when the gunman opened fire in the building.

"Standing guard yesterday at the United States Holocaust Memorial Museum, Mr. [Stephen]Johns was killed while protecting thousands of other inside from the same fate. His death has shocked, upset and angered the Senate, our nation and all who detest such senseless bloodshed," Senate Majority Leader Harry Reid said Thursday.

The gunman exchanged fire Wednesday with guards, including 39-year-old Johns, who died at a Washington hospital from his injuries, police said. Authorities have said 88-year-old James W. von Brunn, a white supremacist, was under investigation in the shooting.

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Sara Bloomfield, director of the museum, described Johns as "a great friend who greeted us every day with a wonderful smile — and he will be missed."

"Obviously, there are no words to express our grief and shock," she said.

Johns worked for Wackenhut Services Inc., which has contracted security services at the museum since 2002, according to a company statement. Johns had been posted at the museum since joining the firm in 2003. The museum has about 70 officers and supervisors on the force.

He grew up in Temple Hills, Md., and still lived in that community with his wife and son after spending a year in New Orleans in the aftermath of Hurricane Katrina, according to Reid.

"Mr. Jones was murdered in a place built to memorialize humanity's most unspeakable murders," Reid said. "He was a victim of violence and hatred in a place dedicated to teaching us the evils of violence and hatred. He was a target of intolerance in a place created for reflection on the consequences of intolerance."

The Holocaust Museum was closed Thursday.

"When it opens tomorrow, and every day thereafter, Stephen Johns' courage and courtesy will be missed," Reid said.

Guards are armed with .38-caliber revolvers and dress in police-type uniforms, the company said. It said preliminary details indicate the officers responded appropriately when facing the gunman, who opened fire with a rifle.

The president and others commended the work of Johns and the other guards.

"We have lost a courageous security guard who stood watch at this place of solemn remembrance," President Barack Obama said in a statement. "My thoughts and prayers are with his family and friends in this painful time."

Washington D.C. Mayor Adrian M. Fenty also had words of praise.

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"The men and women in uniform who put their lives on the line to ensure our safety are truly heroes, and I am deeply saddened that this senseless act of violence threatened the safety of our community," Fenty said in a statement.

Bill Parsons, chief of staff at the museum, said Johns and other guards "did exactly what they were supposed to do to protect people at the museum."

"Never take your guard force and security people for granted," he said.

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The Associated Press contributed to this report.