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We have seen the Twin Towers collapse hundreds of times on TV. The steel and glass skyscrapers exploding like a bag of flour, the dust and smoke pluming out across Manhattan. But never like this, from above.

Nine years after the defining moment of the 21st century, a stunning set of photographs taken by New York Police helicopters forces us to look afresh at a catastrophe we assumed we knew so well.

You know but cannot see the 2,752 men, women and children who died at the World Trade Centre on September 11, 2001. None is visible here.

All we see is the spectacular moment of collapse, what film directors call the wide shot, showing the towers in their urban setting, before, during and after their fall.

Even for those who were there, like me, running from the cloud and choking in the dust, it is hard to believe. But what is all too evident to everyone is that this event changed the world, with consequences that will haunt us for decades.

With the Twin Towers collapsed the world we thought we knew.

These dramatic images were taken by police photographers in helicopters and it is the first time they have been seen, having been released under a Freedom of Information request made by America's ABC News.

Burning buildings can be seen crumpling in on themselves as plumes of smoke rise up over the New York skyline that terrible September morning.

The images show how the police helicopter first began taking images from afar before moving in to reveal the devastation taking place underneath.

They also reveal the horror faced by those trapped in the burning buildings and then the walls of smoke and debris that enveloped the surrounding area as the towers came crashing down.

Released more than eight years after the deaths of 2,752 people on that day, they are powerful reminders of the attack that led to wars in Afghanistan and Iraq.

The legacy of the New York attack continues today with as British forces joining with Afghan soldiers and Nato to launch the biggest attack on the Taliban - accused of harbouring Al Qaeda who organised the 9/11 attack - since the initial 2001 offensive.

Meanwhile, in New York, work is continuing to build on the rubble of what became known as Ground Zero.

Structural steel for the 1,776ft tower, which will be known as 1 World Trade Centre, has already reached 200ft above street level.

Workers are now installing 16 steel nodes on the 20th-floor of the tower which will serve as joints between the steel framing for the building's podium and the steel for the rest of the tower. The 104-storey skyscraper is due to be completed in 2013 and will be one of the tallest buildings in the U.S.