A large number of Americans question what happened that day
It wasn't only the Twin Towers that collapsed on September 11. A third World Trade Center tower that wasn't hit by the planes also fell. As a report into Tower 7 prepares to publish its findings, Mike Rudin considers how this conspiracy theory got to be so big.
9/11 is the conspiracy theory of the internet age.
Put "9/11 conspiracy" into Google and you get 7.9 million hits. Put in "9/11 truth" and you get more than 22 million.
Opinion polls in the US have picked up widespread doubts among the American people.
A New York Times/CBS News poll in 2006 found that 53% of those questioned thought the Bush administration was hiding something. Another US poll found a third of those questioned thought government officials either assisted in the 9/11 attacks or allowed them to happen.
In the UK a survey by the BBC's The Conspiracy Files, carried out by GfkNOP in 2006, found that 16% of those questioned thought there was a "wider conspiracy that included the American government".
For very good reason a lot of people are very suspicious about what went down that day
This summer will be a key moment for those who question the official explanation of what happened on 9/11, the self-styled "9/11 truth movement".
Nearly seven years after the terrible events of that September day, the US authorities are due to publish the final report on a third tower that also collapsed on 9/11. Unlike the Twin Towers, this 47-storey, 610-foot skyscraper was not hit by a plane.
And Tower 7 has become a key issue for "truthers" like Dylan Avery, the director of the internet film about 9/11 called Loose Change.
"The truth movement is heavily centred on Building 7 and for very good reason a lot of people are very suspicious about what went down that day," he says.
Avery points out that Tower 7 housed some unusual tenants: the CIA, the Secret Service, the Pentagon and the very agency meant to deal with disasters or terrorist attacks in New York - the Office of Emergency Management. And some people think Tower 7 was the place where a 9/11 conspiracy was hatched.
FIND OUT MORE...
The Conspiracy Files: 9/11 - The Third Tower is on BBC Two on Sunday 6 July at 2100 BST
The official explanation is that ordinary fires were the main reason for the collapse of Tower 7. That makes this the first and only tall skyscraper in the world to have collapsed because of fire. Yet despite that all the thousands of tonnes of steel from the building were carted away and melted down.
The way official bodies have investigated Tower 7 at the World Trade Center has made some people think they're hiding something. Its destruction was never mentioned in the 9/11 Commission Report.
An inquiry by the Federal Emergency Management Agency said the building collapsed because intense fires had burned for hours, fed by thousands of gallons of diesel stored in the building for emergency generators. But its report said this had "only a low probability of occurrence" and more work was needed. That was in May 2002.
Conspiracy Files: Collapse of WTC 7
The task has now fallen to the National Institute of Standards and Technology (NIST) based at a sprawling campus near Washington DC. For more than two-and-a-half years, scientists there have been studying Tower 7.
Inevitably the officials have been criticised for being slow and even of being frightened to publish.
But the lead investigator at NIST, who heads up their World Trade Center inquiry, Dr Shyam Sunder, says that two-and-a-half years is typically how long an aeroplane crash investigation takes. He added that only in the last few years did they begin to hear criticism from the "truth" movement.
"It's only at the very end in 2005 that this group became more vocal and we found them coming to some of our meetings. But for a long time they were not even present. It wasn't the delay that really caused them, they just woke up one morning and decided to take this on as an issue."
In April 2005, the first thousand DVDs of Dylan Avery's Loose Change movie were pressed. It cost just $2,000 to make. It was a critical moment for the development of the movement. The makers of Loose Change claim it has now been viewed by more than a hundred million people.
Steven Jones, a former physics professor at Brigham Young University, who has become the leading academic voice in the movement, first watched a video of the collapse of Tower 7 in the spring of 2005. But when he did, he said he was taken aback as a physicist.
Will the theories ever be laid to rest?
The American architect Richard Gage's conversion came in 2006 when driving along he heard an independent radio station interviewing the theologian David Ray Griffin.
"I had to do some real soul searching and some research. And the more I discovered the more disturbed I became and realized I was looking for... the architects and the engineers."
Finding that they hadn't really entered the fray by then, Gage decided he had to act.
"It just came to me, I had to start an organization Architects and Engineers for 9/11 Truth."
The fifth anniversary of 9/11 was a huge moment for "truthers". Under the media spotlight protests intensified, websites were spawned and internet films proliferated.
With the publicity also came the "debunkers", challenging the "truthers" at every stage.
After Loose Change came a website called Screw Loose Change. And internet film 9/11 Mysteries was followed by Screw 9/11 Mysteries.
And the "truthers" have fought back. When the US technology magazine Popular Mechanics launched a book called Debunking 9/11 Myths, it was countered with a book by David Ray Griffin called Debunking 9/11 Debunking.
Over time the scale of the alleged conspiracy has grown and grown, encompassing not just sections of the Bush administration, intelligence, but also the fire service, the police, first responders, official investigators, experts, the building's owner, and the media, and, oh yes, even the BBC.
George Bush is hiding something, says the 9/11 truth movement
And over time schisms have opened up in the 9/11 "truth" movement.
So-called "no-planers" believe that commercial aeroplanes did not actually crash into the Twin Towers, the Pentagon or a field in Pennsylvania. Some have suggested lasers from outer space were used.
"Planers" believe aeroplanes were used but argue that only controlled demolitions can explain the collapses of the World Trade Center towers.
Then there are the LIHOPs and MIHOPs. Most "truthers" are MIHOPs - they think the government Made It Happen On Purpose, planning and orchestrating the 9/11 attacks.
But LIHOPs believe the government just Let It Happen On Purpose, to allow them to justify wars in Afghanistan and Iraq and a clampdown on civil liberties.
Into this febrile atmosphere comes the final official report on 9/11.
This summer we will find out whether NIST's report has answered the many questions that have been raised, or whether it will suffer the same fate as the Warren Commission on the assassination of President John F Kennedy and merely add fuel to the conspiracy theories.
Once again lines are being drawn by the use of language in this article. It seems any active questioning of events or suggestions of more feasible explanations are lumped into the category of 'conspiracy theory.' This language unjustly places people into separate camps - those who accept the official story and those who do not. If there are incongruous facts presented to explain these important historical events then we all must question them surely? Does that make us conspiracy theorists? In my opinion this label is too convenient and distracts from any real discourse. I do on the other hand appreciate the presentation of some of the aforementioned incongruous facts relating to Tower 7. Seth Mowshowitz, London, UK
You wrote: "The official explanation is that ordinary fires were the main reason for the collapse of Tower 7. That makes this the first and only tall skyscraper in the world to have collapsed because of fire. "
What you wrote is blatantly untrue, and symptomatic of the problem. The building, while not hit by a plane, was severely damaged by the collapse of the twin towers. There is plenty of photographic evidence of this, but then most conspiracy theorists, like yourselves, obviously haven't looked. Greg Heywood, Wellingborough
I don't think the US govt. is any cleverer than the British one, which can't manage to put in place simple workable systems for taxes, student loans, child support agency, NHS, National Insurance, etc. What makes anyone think they could actually manage a big, unwieldy, secret conspiracy like the one there'd have needed to be for 9/11? Come on, folks - what happened, happened. Simple as that. Joan Bee, England
Your article doesn't mention the context in which the BBC is accused of being part of the cover-up. Is this the issue of the BBC reporting that building 7 had been destroyed due to fire damage before the building had actually collapsed? Then claiming that the tapes from this time 'were missing', refusing to reveal the source of this information or explain how they knew the building was going to collapse before it did? I'm not a conspiracy theorist, I haven't written my own solution to unanswered questions. I (like many others) just want to know the truth. Richard, Birmingham
One has to consider the chain of command were this a government-sponsored act. The sheer number of complicit parties needed would make this impossible without someone having been taken over by the enormity of it and blown the whistle. Conspiracies of silence and lone voices being polished off by the secret services only happpen in Hollywood movies, folks. I guess some people must really struggle to tell the difference between films and real life.
I'm utterly convinced that 9/11 was a tragic day for mankind in which thousands of peple lost their lives because of an audacious and fortuitous terrorist attack, perpetrated by a well-prepared a committed small group. Jon, Chelmsford
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