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(CNN) – Where 110 stories of Twin Towers once reached out to the heavens, today cascading water falls into the void that remains.
This week, more than 12 years on from that horrific day, the National September 11 Memorial Museum will be dedicated and opened to the public on May 21.
Former New York mayor Michael Bloomberg is now chairman of the memorial. He gave CNN's "The Lead with Jake Tapper" a private tour.
"As you go down there are lots of little stories of people who dedicated themselves to, they came for the rescue they stayed for the recovery, and sadly a lot of them got sick from what they had to breathe and have since died or are in the process of battling cancer," says Bloomberg.
Built with private and public funds, the mostly underground museum takes you through step by step, from the planning of the attack to the years-long recovery efforts.
Visitors can see the massive foundation walls that once held up the towers, a fire engine twisted beyond recognition, scraps of what survived from inside the offices, and the steel beam cross that became a symbol of hope in the midst of despair.
There is still a short film titled "The Rise of Al Qaeda" that came under fire from interfaith leaders who said it did not draw a clear enough distinction between practicing, innocent Muslims, and the Islamist extremists of al Qaeda.
"I looked very carefully at the film before we put it up, and then afterwards when people raised the issue. What it clearly says is, we have a responsibility to describe what happened. There's no question that these terrorists evoked God, you could hear their tape recording on the airplane," says Bloomberg.
"But we've got to be very careful, you cannot use this as an excuse to do exactly what they wanted us to do. They wanted us to walk away from giving people the right to practice their religion," said Bloomberg.
"This is a museum and the facts are the facts. To take and brand a billion people with responsibility for what a handful of people did is ridiculous," says Bloomberg.
It was a harrowing traumatic day for millions of Americans. At the time Bloomberg was a candidate for mayor.
"I was reading the newspaper and having a cup of coffee, and somebody said 'oh look at the television.' A small plane had hit the World Trade Center. I looked up, and I'm a pilot, and you could see the gash all across the building. I said that is not a small plane," said Bloomberg.
The primary was that day, and the general election was a few weeks away. But Bloomberg said his "first thought on that day was for the people."
"All you could then do think of is, my God there are people in those buildings, and somebody said to me ... 'There's going to be a lot of firefighters killed in that building,'" Bloomberg said.
In the tension between liberty and security, Bloomberg says he was not concerned that maybe things swung too much toward security.
"Security is one of those things you never know if you have too much, but sometimes you can find out you had too little. I'd rather err on the other side," says Bloomberg.
The remains of more than 40% of those killed on 9/11 have still not been identified. Behind a wall in the museum, the medical examiner's office will continue the daunting work for the families.
On Saturday, the remains were taken solemnly through Manhattan to the memorial, a move that some 9/11 families are unhappy about for a number of reasons.
"It's barbaric, it's inhumane, and it's really un-American," says Sally Regenhard, whose son, a firefighter, died in the attack.
"This is where they belong, this is where it all started and I can't think of a better place to have the office of the chief medical examiner's laboratory to try and identify those who we can," he says. "We can't bring the people back but to the extent you can be assure the survivors that we did everything we could to be respectful of those we lost, I think that's our obligation."
"I want the families to say this is a place to grieve, but the vast bulk of the people here will not be families, they will be from around the world, and you want them to understand the terrible tragedy that 3,000 people were taken from us by a handful of people who didn't like our freedoms. And that we cannot let that happen again," says Bloomberg.