9/11: 'Twin Towers didn't collapse due to fire,' say conspiracy theorists

New York: On September 11, 2001, 2,996 people were killed during one of the deadliest attacks in American history.

The timeline of the 9/11 series of collapse of the World Trade Centre (WTC) buildings is as follows:

8:45 AM: a hijacked American passenger--Boeing 767 crashed into the north tower of the WTC in New York.

The aircraft loaded with 20,000 gallons of jet fuel struck near the 80th floor of the 110- storey skyscraper.

8:59 AM: a second Boeing 767-- United Airlines flight hit near the 60th floor of the south tower.

9:59 AM: The south tower collapsed before the north tower within 10 seconds.

10:28 AM: The north tower collapsed to the ground.

However, a third tower, Tower Seven (WTC7) has been subject to many conspiracy theories as it fell to the ground without actually being hit by a plane.

The 47- storey third tower, located 110 m away from WTC fell to the ground seven hours after the Twin Towers.

Government officials in 2008 stated that the building fell due to "uncontrolled building fires". However, researchers have dismissed these findings, Express UK reported.

An extensive 4-year-study done by professors at the university of Alaska using four very complex computer models suggests that the "fire did no cause the collapse."

The primary conclusion from their report states that fire did not cause the collapse of WTC 7 on 9/11, contrary to the conclusions of National Institute of standards and technology (NIST) and private engineering firms that studied the collapse.

The secondary conclusion suggested that the collapse of WTC 7 was a global failure involving "near simultaneous failure of every column in the building."

Robert Korol, a leading conspiracy theorist, a civil engineer and author of architects and engineer for 9/11 truth, also dismissed the official findings and claimed that the the destruction of the twin towers was caused by "controlled demolition"

According to Korol, "it didn't make sense" how the towers collapsed. "Indeed, neither before nor since 9/11 have fires cause a total collapse of a steel- framed high rise -- nor has any other natural event, with the exception of 1985 Mexico City earthquake which toppled storey office building, Express UK reported.

Controlled demolition is a procedure whereby explosives or other devices are used to bring down a structure intentionally.

Another point of contention made by the professor was that the fires would not have been strong enough to burn through the steel structures.

He said, "The fires were on the upper floors, there's little chance the heat would have spread down and caused the steel columns or connectors or floor beams, to sufficiently weaken and collapse in the twin towers."

He also said they were treated with a fire retardant which would have insulated them.

The NIST in charge of the official report had concluded fire to be the reason of the collapse of twin towers.