The mystery surrounding the third tower that collapsed on 9/11 known as World Trade Center Seven (WTC7) has been central to many conspiracy theories because the skyscraper fell to the ground without being hit by a plane.
The 47-storey third tower, located 110 meters (350 feet) away from the World Trade Centre, collapsed in just 2.5 seconds, seven hours after the twin towers collapsed.
Despite calls for the evidence to be preserved, New York City officials had the building's debris removed and destroyed in the ensuing weeks and months, preventing a proper forensic investigation from ever taking place.
WTC7 after the twin towers collapsed.
Seven years later, federal investigators concluded that WTC 7 was the first steel-framed high-rise ever to have collapsed solely as a result of normal office fires.
In 2008 The National Institute of Standards and Technology (NIST) in charge of the official report concluded that fire was the explanation for the collapse.
It stated that the building was brought down by fires inside the building that were caused be debris that fell into it from the collapsing twin towers.
NIST Video: Why the Building (WTC7) Fell
However a comprehensive 127 page report compiled by Institute of Northern Engineering researchers has refuted the “official story” regarding the 9/11 and WTC7.
According to the study which was released by researchers at the University of Alaska Fairbanks (UAF) following a four-year computer modeling study, they concluded that it was scientifically impossible for fires to bring down WTC7.
UAF civil engineering professor Leroy Hulsey was the study's principal investigator. Feng Xiao, now an associate professor at Nanjing University of Science and Technology, and Zhili Quan, now a bridge engineer for the South Carolina Department of Transportation, were research assistants and co-authors.
The research team produced a simulation that replicated the structural fire loading conditions of WTC7 on September 11, 2001, supplemented by data from the National Institute of Science and Technology’s collapse initiation hypothesis.
UAF video: Fire Did Not Bring Down Building 7 on 9/11
The researchers have dismissed the findings of Government officials in 2008 that the building fell due to “uncontrolled building fires”.
Following an extensive four-year study at the University of Alaska, using four extremely complex computer models, Dr. Leroy Hulsey, Dr. Zhili Quan, and Professor Feng Xiao found the fire did not cause the collapse.
"Our study found that the fires in WTC 7 could not have caused the collapse recorded on video," said Professor Hulsey.
"We simulated every plausible scenario, and we found that the series of failures that NIST claimed triggered a progressive collapse of the entire structure could not have occurred. The only thing that could have brought this structure down in the manner observed on 9/11 is the near-simultaneous failure of every column in the building below Floor 17."
Dr. Leroy Hulsey presented the findings and conclusions detailed in his team’s progress report.
The UAF study was funded by Architects & Engineers for 9/11 Truth (AE911Truth), a nonprofit representing more than 3,000 architects, engineers and academics led by professor Robert Korol, a civil engineering professor, who have signed the organization's petition calling upon Congress to open a new investigation into the destruction of the three World Trade Center towers on 9/11.
So the question remains, if fire did not bring down WTC7 on 9/11, what caused a 47-storey skyscraper to collapse in just 2.5 seconds?