The final mystery of 9/11 will soon be solved, according to US experts investigating the collapse of the third tower at the World Trade Center.

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.