Experts probing the collapse of a third World Trade Center tower are expected to announce that fires brought it down, the BBC reports. The tower, known as WTC7, fell hours after the Twin Towers came down. No steel-framed skyscraper has ever collapsed due to fire, and a group of scientists, engineers, and architects maintain that a controlled demolition destroyed it.
"Building 7 is the smoking gun of 9/11," said the head of the group. But investigators from the National Institute of Standards and Technology say the unique collapse was due to the building's unusual design, and the fact that its fires burned far longer than past skyscraper blazes, while Sept. 11 firefighters devoted resources to saving lives.