An unresolved mystery of 9/11 is the collapse of the World Trade Center building 7, hours after the collapse of WTC-1 and WTC-2, as it was never hit by a plane, Press TV's US Desk reports.
Scientists, architects and engineers all over the world have questioned the official version of how WTC-7 fell down, adding that these buildings are built to fight even the formidable forces of nature.
Based on claims by the US government, the 47-story modern steel-framed WTC-7 was brought down by office fires.
Shyam Sunder, the lead investigator at National Institute of Standards and Technology (NIST) -- a state-run organization -- had said, “World Center 7 collapsed because of fire fueled by office furnishings.”
However, experts say that a building with a steel-frame never collapses after a few hours of fire.
“Fires have never before caused the collapse of any skyscraper. Even though there are numerous examples of much hotter, larger, and longer-lasting fires in these buildings,” says architect Richard Gage, the founder of AIA Architects.
Metallurgical engineer Kathy McGrade says, “You cannot generate enough heat to melt steel.”
According to witnesses, massive explosions were heard before WTC-7 collapsed.
NIST's official scenario resulting in the total collapse of the building is, as experts say, absolutely impossible.
All the columns needed to be severed at the same time in order for that structure to fall the way it did, based on what structural engineer Michael Donly says.
Although NIST rejected the possibility of any sort of controlled demolition, it refused to test the explosive residues, which could have documented the evidence of melted steel.
“The destruction of evidence was a criminal act itself. It was already being carted away and destroyed when the investigators got there,” says structural engineer Ronald Brookman.
Families of the victims demand that the cause of the collapse be investigated carefully because millions of people around the world, and not just scientists and engineers, want these unanswered questions answered.