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US President Barack Obama has led an emotional dedication of a museum that commemorates the traumatic events of Sept. 11, 2001, built on the "ground zero" site of the twin towers that fell that day.
Obama and his wife, Michelle, joined by Bill and Hillary Clinton and former New York Mayor Michael Bloomberg, toured the museum, which includes artifacts from many of the nearly 3,000 people who died in the hijacked-plane attacks in New York, Washington and Shanksville, Pennsylvania.
"Here we tell their story so that generations yet unborn will never forget," Obama said in dedicating a museum that he called "this sacred place of healing and hope."
The ceremony was held in a cavernous, underground hall where what remains of the foundation of the twin World Trade Center towers can still be seen, along with a retaining wall that survived the blasts.
In the center of the room, a 36-foot-high column covered with posters of those missing after 9/11 and names of units of fire and emergency workers who died responding to the tragedy.
Obama singled out 9/11 victim Welles Crowther, a 24-year-old equities trader known simply as a man wearing a red bandana who saved a dozen lives on the South Tower's 78th floor. His body was recovered at ground zero in 2002.
A red bandana of the type he wore that day is displayed at the museum, donated by his mother, Allison, who spoke at the ceremony along with Ling Young, a woman Welles led out of the building.
Also on display is the charred watch worn by Todd Beamer, the software salesman who led a passenger revolt against the hijackers on United Airlines flight 93 before it crashed into a field near Shanksville.
The museum includes emotional telephone messages left for loved ones by those who would die in the towers, and cockpit recordings from the doomed planes.
During the tour, the Obamas walked through a hall with row upon row of photos of those who perished: old, young, some in firefighter and police uniforms, before entering a hall inscribed with Virgil's "No day shall erase you from the memory of time."
They paused beside what was left of a fire truck, scarred by flames, its ladders twisted beyond recognition.
Obama said the memorial "reaffirms the true spirit of 9/11 - love, compassion, sacrifice, and enshrines it forever in the heart of our nation."
"I think all who come here will find it a profound and moving experience," he said.
Obama noted that it was three years ago this month that "our SEALS made sure that justice was done," a reference to the secret U.S. mission he ordered that killed 9/11 mastermind Osama bin Laden in his Pakistan hideaway.
"Nothing can ever break us. Nothing can change who we are as Americans," Obama said.