Before the dust had settled Osama bin Laden claimed that Al Qaeda operatives were responsible for hijacking four American commercial jet airplanes and flying three of them into the WTC and the Pentagon. The fourth jet crashed in a field in Pennsylvania after passengers fought hijackers for control of the airplane.

The immediate media version of events was that the jet fuel on the planes caused fires inside the building that fatally compromised the structural integrity of the towers and caused their collapse about an hour after impact.

While there are many “doubting Thomas’s” regarding the official verdict, the most prominent group is the “9/11 Truth and Justice Movement.” Members are known as “truthers.”

The truthers are a diverse lot: left wing opponents of the bygone Bush administration; left wing and right wing opponents of Israel; families of those who died in the WTC collapse; academics; arch-conservatives; far right extremists; far left extremists; scientists; architects; physicists; and so on. What unites them is a belief our government has not told everything it knows about the 9/11 attacks.

Within this broad belief are numerous varieties of opinion. Theories range from the plausible to the incoherent. For instance, claims that corporate America, big oil, Bush family ties to the Skull and Bones society, the CIA, the Freemasons, the Jesuits, the Illuminati, and even the BBC were either behind the plan, flying the planes, shooting laser guns, detonating explosives or nuclear weapons, or trying to cover everything up.

Some truthers believe Mossad (Israel’s version of the CIA) was behind the acts of terror in order to spur the United States into attacking Israel’s enemies (i.e, most of the Middle East). Other truthers go farther out on a limb in claiming the 9/11 attacks are part of Israel’s plan to make Zionism a worldwide power. This seemingly fantastic theory has surprising traction outside of the United States.

Then there are the “planers,” who believe planes crashed into the WTC, and “no-planers,” who do not believe planes were used in the attack. Instead they claim lasers or some form of nuclear detonation laid the towers low. And let’s not forget the MIHOPS (the government Made It Happen On Purpose, that is, participated in the attacks) and the LIHOPS (the government Let It Happen On Purpose).

The prevailing truther theory of the WTC collapse, however, is controlled demolition. This theory is based on the similarity in how the twin towers collapsed and how planned demolitions of buildings in populated areas occur. Controlled demolition causes the structure to implode upon itself, thereby reducing the risk of harm to nearby buildings and people.

Another truther group, Scholars for 9/11 Truth and Justice (STJ), claims to have eyewitness accounts of loud explosions and light flashes on the ground immediately before the towers collapsed. Dr. Steven Jones claims to have found traces of thermite on the dust in the rubble of the twin towers collapse.

Recently this theory was endorsed by an unusual source. Mahmoud Ahmadinejad has a PhD in Transportation Engineering and Planning. He is also the president of Iran. He publicly declared it was impossible for two jetliners to bring down the towers simply by hitting them, so some sort of planned explosion must have taken place. President Ahmadinejad’s opinions drew a harsh rebuke from – of all places – Al-Qaeda, who said Ahmadinejad’s claim was “a ridiculous belief that stands in the face of all logic and evidence.” Al-Qaeda also complained that Iran was supporting the theory that Israel planned the attack on the two towers.

Who else might profit from destroying the World Trade Center? In 2006 STJ spokesmen claimed a cabal of American neo-conservatives – Dick Cheney and Donald Rumsfeld are the big names – hatched a plan for US domination of the world, which they named Project for a New American Century (PNAC). STJ accused PNAC of planning the 9/11 attacks to justify future American efforts to control or conquer Afghanistan, Iraq, and Iran. This claim has proven easier to make than to prove.

In recent years truthers are being confronted by another group called “debunkers.” The debunkers dedicated themselves to disproving the truthers conspiracy theories – the science, not the geopolitics. This brings us once again to the theory of controlled demolition.

Debunkers point out that a demolition project for the WTC towers would require thousands of pounds of explosives and ignition devices to be placed inside the walls on each face of each tower on all the lower floors. The demolition team would have to cut through walls on all these floors of the WTC, somehow get thousands of pounds of explosives past security, and seal the walls back up without anyone noticing the noise or the mess.

Debunkers note that film of the towers collapsing shows the collapse began on the higher floors, where the planes hit the tower. The collapsing floors pancaked on top of the lower floors, picking up momentum as they fell. In a controlled demolition, the collapse begins at the bottom, not the top.

A little known fact is that on the morning of 9/11 a private demolition firm, Protec Documentation Services, ran seismographs on construction sites in Lower Manhattan. The machines recorded the tremors of the towers falling, but there were no readings of prior ground vibrations that should have occurred from a controlled demolition at the bottom of the towers.

Another argument from some truthers is that the jet fuel induced fires were not hot enough to melt the steel beams supporting each tower. Truthers like Dr. Jones claim there is evidence of thermite in the wreckage, which would support the controlled demolition theory.

Debunkers argue back that massive amounts of thermite would have had to been snuck into the WTC and placed in walls just like the explosives were, without attracting any attention from the thousands of employees working in the building. Furthermore, steel need not be liquefied in order to give way. Heat under 2,000 degrees can still damage, bend, or otherwise compromise steel structures. So can the impact of a commercial airplane slamming into it.

The truthers and debunkers have been going at it for several years now. In following the arguments much can be found out about how concrete and steel react to fire and trauma, and the nature of jet airplane crashes. The ill will between the groups is palpable. 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.

In a national phone poll taken recently, more than one third of the responses indicated belief the federal government was either part of the attack or knowingly allowed it to happen. Sixteen percent believed there was a controlled demolition.

Whatever one believes about 9/11, perhaps we can all agree that the group with the greatest interest is a quieter group: those who have lost family and friends in the WTC collapse. They have persistently lobbied for answers to many questions they have, and have been disappointed by the federal government’s response, and by the refusal of a New York state judge to allow their petition for another investigation to be voted on by citizens of new York. They also have a website (9/11 Family Steering Committee). Their points of view are as varied as their shades of grief.