GETTY The Twin Towers were hit by planes but conspiracy theorists claim bombs brought them down.

While many of the theories are bizarre, one longstanding view is the towers would not have collapsed in the way they did if they were hit by aircraft. Some claim there must have been a "controlled detonation" at ground level for the Twin Towers to fall in on themselves as they did. One key part of their argument is the collapse of a third smaller tower, called Building 7, at the World Trade Centre complex, several hours after the huge skyscrapers fell. Until now, the theory has been just that and confined to the online forums of conspiracy theory websites. But now, the University of Alaska is sponsoring a full investigation into claims that World Trade Center Building 7 was brought down by a controlled demolition during the 9/11 attacks.

The official version of events is that fire spread to Building 7, from the main towers, devastating the structure, and causing it also to fall in on itself. Footage of the tower consumed by fire emerged in 2011, and it was thought the conspiracy may have been killed off. But Dr J Leroy Husley, chair of the University of Alaska Fairbanks’ (UAF) Civil and Environmental Engineering Department, has partnered with architects and engineers linked to campaign group 9/11 Truth to evaluate the causes of its collapse. A report on Activistpost.com said: "Although questions still remain about how the two planes that hit the Twin Towers could cause the total collapse of the high-rise buildings, many 9/11 researchers now focus on the mysterious collapse of Building 7. "A number of 9/11 family members point to the collapse of WTC7 as a possible crack in the official story that could spark a new national conversation on the events of that day.

YouTube Building 7 as it starts its collapse hours after the towers fell.

A completely open and transparent investigation into the cause of World Trade Center Building 7’s collapse. 9/11 Truth spokesman

“WTC7 was not hit by a plane that day; however, it collapsed at 5:20 p.m. according to the National Institute of Standards and Technology (NIST), the official cause for the collapse was office fires. “A growing number of family members, activists, architects and engineers question the official theory for collapse and are seeking a new investigation into WTC7." Dr Hulsey and the WTC7 Evaluation project hope to answer some of the remaining questions. The project is a two-year study that is being crowd-funded through Architects & Engineers for 9/11 Truth. Dr Hulsey has invited professionals from the fields of structural engineering, civil engineering, mechanical engineering, architecture, building design and construction, physics, maths, and science, as well as everyday citizens, to get involved. He said: "Over the next year, with a team of PhD students, I will be rebuilding World Trade Center building 7, using the same drawings that were used to build it originally we will reconstruct it digitally. “NIST says the building fell down due to office fires. Our investigation will evaluate the probability that this was the cause of the collapse.”

9/11 Terror Attacks - Seen from the sky Wed, February 10, 2010 Stunning new pictures of the 9/11 terror attacks on New York as seen from the sky Play slideshow 1 of 16 These stunning new pictures of the 9/11 terror attacks in New York were taken by a police helicopter and have just been released to the public