How 9/11 became a hotbed for conspiracy theories that experts STILL have to debunk years later

From the earth-shattering moment that hijacked commercial airliners were flown into the World Trade Center towers on September 11, 2001, questions were immediately raised. 

How could two of the most iconic skyscrapers in the world be such vulnerable targets? Why did the towers collapse under their own weight? Were the buildings rigged with explosives?

For investigator David Dunbar, one of the authors behind Popular Mechanics' widely-cited 2005 takedown of many such theories, the decades since the tragedies have been maddening. 

'There seemed to be little interest on the part of the conspiracy theorists to do any fact-checking for themselves,' Dunbar told the Daily Mail this week, ahead of the 25th anniversary of the attacks.

'But if people don't want to be don't want to be convinced by verifiable facts, if they're so invested psychologically, emotionally, spiritually, in every way with this alternative worldview, then they're not going to be receptive to the findings of an expert who, for example, proves that steel doesn’t have to melt to lose its structural strength.'

The roots of the 9/11 conspiracy world can be traced back to right-wing firebrand Alex Jones, who rose to infamy in the aftermath of the attacks with his self-branded '9/11 truther' movement. 

Jones said on his radio show just hours after the attacks that he believed the Twin Towers collapsed due to a controlled demolition, and he quickly organized public protests accusing the Bush administration of orchestrating the tragedy. 

The movement's success led Dunbar's team of engineers to delve into the claims, and they worked with a slate of researchers, investigators and aviation experts with the National Institute of Standards and Technology (NIST) to analyze the skyscrapers' mechanics. 

From the earth-shattering moment that hijacked commercial airliners were flown into the World Trade Center towers on September 11, 2001, questions were immediately raised

'Jet fuel doesn't melt steel beams' 

In the most widely propagated conspiracy theories surrounding the Twin Towers, skeptics claim that the ultimate collapse of the skyscrapers would not be possible. 

They claim that the planes struck too high on the structures to cause collapse, with first impact on the North Tower crashing through the 94th to 98th floors, and the second impact on the South Tower hitting between the 78th and 84th floors.

But NIST investigators cited in Popular Mechanics' takedown found in a 2005 study that the collapses were triggered by the planes slicing through utility shafts in the towers' core.

This created a vent of burning jet fuel, igniting the inner chamber of the buildings for 56 minutes before the structures caved in within six minutes of each other. 

The issue of the jet fuel from the aircrafts also spawned one of the most well-known lines peddled by Jones - that 'jet fuel doesn't melt steel beams.'

Skeptics argue that jet fuel's top burning temperature of 1500 degrees Fahrenheit doesn't reach steel's melting point of 2750 degrees Fahrenheit. 

In the most widely propagated conspiracy theories surrounding the Twin Towers, skeptics claim that the ultimate collapse of the skyscrapers would not be possible from being struck by airplanes 

Dunbar explained that while this is true, the steel frames of the Twin Towers did not need to melt for them to collapse - they merely had to lose their structural strength, which caused the steel support beams to bend and buckle.

'The main theories focused on the Twin Towers and World Trade Center 7, and the melting steel seemed to be easy for the general public to grasp,' Dunbar told the Daily Mail, as he explained why much of his debunking focused on claims surrounding the Twin Towers collapse. 

'The destruction of the World Trade Center buildings was studied by experts for years. Their conclusion was consistent: The combination of the damage from the airplane impacts and the prolonged fires ultimately destroyed the structures. 

'But I guess that wasn't too interesting to conspiracy theorists. It was sexier to go from not hot enough to melt steel to, therefore, a controlled demolition to, therefore, an inside job.' 

Steel loses roughly 50 percent of its strength at 1100 degrees Fahrenheit, and Popular Mechanics noted in its piece that combustible material inside the buildings - such as rugs and furniture - brought the temperatures to over 1800 degrees Fahrenheit as they acted as kindling for the flames. 

Forman Williams, a professor of engineering at the University of California, San Diego, and a structural engineer that Popular Mechanics consulted in its research, explained in the piece: 'The jet fuel was the ignition source.

'It burned for maybe 10 minutes, and [the towers] were still standing in 10 minutes. It was the rest of the stuff burning afterward that was responsible for the heat transfer that eventually brought them down.'

'The towers were a controlled demolition' 

When the towers eventually collapsed, footage showed visible puffs of dust and debris ejecting from the floors as they collapsed on top of each other. 

Skeptics claimed that this was evidence of explosives inside the floors, set off to bring the building down in a controlled demolition. 

When the 'controlled demolition' theory first gained traction, Van Romero, an explosives expert and vice president of the New Mexico Institute of Mining and Technology, was quoted by the Albuquerque Journal as saying it was caused by 'explosives.' 

He was reported as stating that 'there were some explosive devices inside the buildings that caused the towers to collapse' - which became a widely-cited quote among skeptics, and which Romero later told Popular Mechanics was not true. 

The quote was fodder for skeptics for years, but Romero said he was misquoted, insisting he never believed explosives brought down the building, and 'I only said that that's what it looked like.'

The roots of the 9/11 conspiracy world can be traced back to right-wing firebrand Alex Jones, who rose to infamy in the aftermath of the attacks with his self-branded '9/11 truther' movement

Researchers say the massive energy transfer through the building caused each floor to 'pancake' onto the next, and the huge volume of air inside the structure was ejected along with concrete and debris. 

'When you have a significant portion of a floor collapsing, it’s going to shoot air and concrete dust out the window,' NIST lead investigator Shyam Sunder told Popular Mechanics. 

Sunder conceded that the effect has a similar appearance as small explosions, 'but it is the floor pancaking that leads to that perception.'

Dunbar said he felt debunking these specific claims was important for his team's research, as 'conspiracy theorists thought this was proof of a controlled demolition.'

'The puffs of dust and other debris ejected from the sides of the buildings during collapse were the result of floors pancaking on top of each other with tremendous energy,' he said. 

'The compressed air, pulverized concrete, and other material went out windows and took any other path of least resistance it could find.’ 

Dunbar said his team consulted the owner of a demolition company in their study, and asked him, 'If you wanted to bring down the World Trade Towers with a controlled demolition, what would it take?'

The explanation convinced his researchers of the impossibility, he explained. 

First, according to the owner, the explosives for such a demolition did not exist. Second, if someone attempted to make such charges, they’d weigh thousands of pounds apiece and require forklifts to bring them into the buildings. 

Third, it’d take a crew of 75 up to two months to strip the fireproofing from the box columns at the base of the buildings and then place and wire the hypothetical charges - all done covertly while some 50,000 workers in the two towers went about their daily business.

As for smuggling explosives to upper floors and hiding them, according to the owner they might blow out windows, but they would not knock the buildings down. ‘Typically, you don't even place detonations on the upper floors, you place them on the ground floor or basement and let the building's own weight bring it down.

‘So the idea that there would be somehow a team of demolition experts who go in the building after everybody's gone home for the day and start planting detonation devices... I mean, it was just absurd.

‘It just revealed a real lack of research on the part of the conspiracy theorists and a lack of understanding of the basics of this kind of work.‘