President Bush's chief counter-terrorism adviser on 9/11, Richard Clarke, told The Conspiracy Files that there are two key reasons he thought the conspiracy theories about 9/11 are not possible - first competency, the alternative theories suggested are hugely complex and would have required a huge number of people; secondly, the difficulty of keeping secrets.
The more high profile and outrageous the act the more difficult to keep it secret. Richard Clarke added that in all the 30 years he'd had top level intelligence clearance nearly all the key secrets he'd seen had become public.
The former counter-terrorism adviser is adamant that the theories that a third tower, called World Trade Center Building 7, was brought down by a controlled demolition is not possible:
"Hundreds of people thousands of people would have had to have been involved and know about it and it most surely would have leaked out."
One of the comments on the blog raised the Iran Contra conspiracy as evidence that in fact you don't need hundreds or thousands of people to carry out a very complex conspiracy. Iran Contra is a good example because it shows clearly that conspiracies do happen. They can be complex.
But the Iran Contra conspiracy was exposed. And what's more, as it went on it necessarily began to drag in more and more people.
Richard Clarke also made the point that any conspiracy on 9/11 would have been unbelievably risky for Bush or Cheney:
"The risk to them would be personally, that they would go to jail for the rest of their lives. That they would have their name blackened throughout history, and that their political party would be destroyed. Everything that they had ever worked for their party for their family, for themselves, would be utterly smashed."
Other comments have suggested that it is wrong to mention that critics have suggested that the BBC and other sections of the media were allegedly involved in a conspiracy. If you read the many comments on this blog it is clear that people are suggesting just that.
Yet once again those suggestions draw in hundreds and thousands more people. Every time more people are drawn in it makes the chances of keeping anything secret even more difficult.
The long awaited final report on Tower 7 at the World Trade Center is due later this month and the American government hopes it will provide the answers to the questions that have been raised about that building.
This is likely to be the government's last word on 9/11. Those who continue to question the official explanation have still to set out what exactly the grand conspiracy was, how it was carried out, who carried it out and why they would do so.
The Conspiracy Files: 9/11 - The Third Tower repeated on Tuesday 8 July at 2320 BST BBC Two