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.
Terror: A tidal wave of dust and debris roars through lower Manhattan as the World Trade Centre collapses on September 11, 2001
Collapse: This image captures the sheer size of the debris cloud enveloping buildings and cars as the towers collapse
The cloud spreads out, consuming the surrounding area and moving out over the East River