The 47-storey third tower, known as Tower Seven, collapsed seven hours after the twin towers. Investigators are expected to say ordinary fires on several different floors caused the collapse. Conspiracy theorists have argued that the third tower was brought down in a controlled demolition. Unlike the twin towers, Tower Seven was not hit by a plane. The National Institute of Standards and Technology [NIST] ... is expected to conclude in its long-awaited report this month that ordinary fires caused the building to collapse. That would make it the first and only steel skyscraper in the world to collapse because of fire. [NIST's] lead investigator, Dr Shyam Sunder, spoke to BBC Two's The Conspiracy Files": "Our working hypothesis now actually suggests that it was normal building fires that were growing and spreading throughout the multiple floors that may have caused the ultimate collapse of the buildings." However, a group of architects, engineers and scientists say the official explanation that fires caused the collapse is impossible. Architects and Engineers for 9/11 Truth argue there must have been a controlled demolition. The founder of the group, Richard Gage, says the collapse of the third tower is an obvious example of a controlled demolition using explosives. "Building Seven is the smoking gun of 9/11. A sixth grader can look at this building falling at virtually freefall speed, symmetrically and smoothly, and see that it is not a natural process. Buildings that fall in natural processes fall to the path of least resistance", says Gage, "they don't go straight down through themselves."