4 corners 911 conspiracy fanatics

On tonight ABC at 8:30 pm

Seven years on, the destruction of New York's Twin Towers, played and replayed thousands of times over, is seared into collective memory.

A third skyscraper also fell that day. Unlike the Twin Towers, the 47-storey building known as Tower Seven was not hit by a fuel-laden plane, yet it collapsed neatly in 6.5 seconds.

The official explanation is that it was destroyed by fire. But in the seven years it has taken to present the final investigation report, suspicion has filled the information vacuum. Tower Seven has fed an industry of conspiracy theories that grew up around 9/11. Claims are pressed – by a phenomenally popular movie on the Internet and by supposedly credible "experts" – that someone in or close to the US Government brought the building down by controlled demolition.

How, among the many questions they ask, could Tower Seven be the first and only steel-framed skyscraper in the world to collapse due to fire? Why did the New York fire department not fight the fires? Why did it fall so symmetrically at freefall speed? Why did TV stations report that Tower Seven had collapsed before it had done so, when it was still clearly visibly behind reporters?

This BBC documentary explores some of these questions. In doing so it demonstrates how, when good information is scarce, or late, many people will believe the worst. "9/11: The Third Tower" – on Four Corners 8.30 pm Monday 8 September and 11.35 pm Tuesday 9 September (also 8am Tuesday on ABC2).