Theories about what really happened on 11 September, 2001 continue to inspire books and documentaries and convince otherwise sane, respectable public figures, not to mention the teeming masses. Journalist Robert Fisk recently joined the fray, intrigued by the scientific improbably of the buildings collapsing in such a seemingly controlled way and charges by engineering professors who call the final report "fraudulent or deceptive". As a Middle East expert, he also finds the letter allegedly written by Mohamed Atta, the Egyptian hijacker- murderer "weird", surely a forgery.

Another recent convert, University of Massachusetts Geoscience Professor Lynn Margulis referred to 9/11 as "this new false-flag operation, which has been used to justify the wars in Afghanistan and Iraq as well as unprecedented assaults on research, education, and civil liberties", and credited The New Pearl Harbor by David Ray Griffin "which provides overwhelming evidence that the official story is contradictory, incomplete, and unbelievable."

Robert M Bowman, the former head of the Star Wars missile defense programme under former US leaders Gerald Ford and Jimmy Carter figures the main suspect is Vice-President Dick Cheney, that the military command structure may not have been aware that the drills on the morning of 9/11 to simulate planes crashing into buildings on the east coast were actually a cover to dupe unwitting air defence personnel into not responding quickly enough to stop the attack.

9/11 itself has perforce become a thing of legends, because all evidence quickly disappeared from the scenes of the tragedies in New York and Washington: the steel from the World Trade Center now recycled and reimported as Chinese toaster ovens, and where are the bits of the Boeing 757 that crashed into the Pentagon? The official 9/ 11 Commission investigation pointedly ignored reams of damning testimony, and key witnesses have been silenced by gag orders or just ignored, so it appears more and more likely that we will never ever know what exactly happened, who knew, who planned it all, who carried it out, and why.

There are more versions of what might have happened than you can shake a stick at, and are divided into LHOP (let it happen on purpose) and MHOP (made it happen on purpose). The most far-fetched ones, such as the theory the planes that supposedly hit the WTC were actually hologrammes, are used to pooh-pooh any talk of conspiracy at all, ignoring the fact that the biggest conspiracy theory -- and most far- fetched one -- is the official version, which less than one- quarter of respondents agreed with in a recent opinion poll in New York.

One of the earliest critiques, L'Effroyable Imposture (The Horrifying Fraud) by Thierry Meyssan, became a bestseller in Europe in 2002, and was the first to argue that the Pentagon was struck by an air-to-ground missile fired by the US Air Force, with wars in Afghanistan and Iraq and oil as the motives.

The farcical 9/11 Commission prompted the formation of a 9-11 Citizens Commission in 2004 where Congresswoman Cynthia McKinney testified. The first demonstrations "Bush did it!" started in 2002 across the US and over six million "Deception Dollars", claiming 9/11 was an inside job, have been distributed since then at various demonstrations. A "European United for Truth" march taking place in Brussels on 9 September is the latest European protest. The most popular organisations include the 9/11 Truth Movement formed in 2004, an umbrella of dozens of grassroots organisations, with its own Internet portal 911truth.org. There is an array of scholars, architects, engineers, veterans for 9/11 Truth in the United States and abroad, and even a Journal of 9/11 Studies.

A slew of recent documentaries have added weight to the many books already published. The video documentary Loose Change is one of the true miracles of the Internet. Director Dylan Avery put together this powerful challenge to the establishment for a few thousand dollars and it has already been downloaded over four million times. Charlie Sheen recently agreed to provide the voiceover for a future cinema release. It starkly relates the many smoking guns. Alex Jones's Martial Law -- 9/11 argues that from Nero burning Rome to Hitler burning the Reichstag, power-mad leaders through time have manufactured crises in order to present the public with situations "where their police state solutions 'make sense'. Give up your rights -- it's for your safety." Others include Barry Zwicker's The Great Deception and George Humphrey's The Grand Illusion.

But these Western efforts stick to the theory that it was a US plan, with oil and political control by right-wing forces as the motive. Only the unofficial Muslim world pointed the finger at Israel from the start. Is it possible Mossad infiltrated (or itself organised) Muslim terrorist cells and carried out the attacks?

As the WTC burned and crumpled, five men, movers with Urban Moving Systems, an Israeli company and very likely a Mossad front group, celebrated and filmed the atrocity. At least two of them were Israeli intelligence agents, working for Mossad. They were arrested and eventually deported at the end of November 2001 under suspicious circumstances. There is little doubt now that Mossad was spying on Arab extremists in the US and knew the attack was in the offing. 140 Israelis were detained prior to 11 September, 2001, as part of a widespread investigation into an Israeli espionage ring, the infamous "Israeli art students". Following 9/11, 60 more Israelis were arrested.

After the attacks on New York and Washington, former Israeli Prime Minister Benyamin Netanyahu was asked what the terrorist strikes would mean for US-Israeli relations. He said: "It's very good." Then he corrected himself, adding: "Well, it's not good, but it will generate immediate sympathy [for Israel from the Americans]." According to the official Israeli 9/11 memorial site, only three Israelis died in the WTC (one was a deaf janitor); one elite commando was aboard Flight 11 and a woman was aboard United 175 which hit the WTC. Then there are the Odigo messages Israelis got two hours before the events, warning them not to go to the WTC. Cui bono anyone?

Whatever the real story behind 9/11, history is littered with real and imagined conspiracies, especially where the Cold War was concerned. We can laugh in retrospect at attempts to poison Fidel Castro's cigars but the great turning points in the past half century where militarism triumphed have all contained elements of conspiracy. In each case mass peace movements created pressure on politicians to resist militarism, yet the right was able to triumph. When necessary, using subversion and conspiracy. Sometimes, by merely latching onto imagined threats.

Leaving aside the assassination of president John F Kennedy, who was purportedly about to pull out of Vietnam and end the Cold War, consider the fateful year 1979. The US was still reeling under the anti-war movement and the public revulsion to all things military following Vietnam, and was forced to sign major disarmament treaties and cooperate with the Soviets, coming very close to ending the Cold War, at least publically. The Apollo-Souz space programme was the most visible manifestation of this. The Olympics were about to be held in Moscow, when the world was suddenly shocked by the Soviet invasion of Afghanistan.

The real story behind this was that the US had secretly begun a programme of covert aid to the Afghan guerrillas six months before the Soviets invaded. Former CIA director and current Minister of Defense Robert Gates in his 1996 memoir From the Shadows revealed that peace-loving president Carter approved a secret $500 million aid programme designed to counter the Soviet support to the pro-Soviet regime that had overthrown the dictator Mohamed Dawoud Khan (who had just overthrown his cousin, King Mohamed Nadir Shah) in Kabul.

According to Gates, at a meeting on 30 March, 1979, Under-Secretary of Defense Walter Slocumbe suggested "there was value in keeping the Afghan insurgency going, 'sucking the Soviets into a Vietnamese quagmire'." Carter, who authorised the covert programme on 3 July, 1979, today explains that it was definitely "not my intention" to inspire a Soviet invasion. Was this also a conspiracy, with naïve Jimmy a dupe? LHOP or MHOP? Either way, it created the foundations for the greatest military build-up that the world has ever seen, as Reagan won a landslide election on the promise to deposit the SU in history's rubbish bin. Oh, it also created Al-Qaeda.

Unfortunately for the right, Reagan's success had its downside. With the collapse of the Soviet Union, the American war machine lost its raison d'etre and the world expected a peace dividend, a dismantling of both the Soviet and US arsenals and an end to the unending arms race. The Cold War was finally over, the "enemy" defeated. Funny how 9/11 came along just in time.

The CIA's 1962 Operation Northwoods to create and utilise bogus terrorist attacks against the US substituting real commercial airliners with pilotless drone aircraft.

- The 2000 Project for the New American Century report Rebuilding America's Defenses mentioning "some catastrophic and catalysing event -- like a new Pearl Harbour."

- Also in 2000 the first of two training exercises conducted which simulated a Boeing 757 crashing into the WTC. The second "exercise" was scheduled for the exact time that the 9/11 events occurred.

- From 6-10 September 2001 an unusual amount of put options placed on American Airlines, Boeing and United Airlines stock.

- Bin Laden's denial of involvement in a statement on 16 September: "The United States should try to trace the perpetrators of these attacks within itself; to the people who want to make the present century a century of conflict between Islam and Christianity."