The world reeled with shock and horror as the World Trade Centre twin towers collapsed in New York on September 11, 2001.
Nine years later, scientists, skeptics and interested citizens still struggle to agree on the physical principals of how the buildings collapsed.
Engineers and computer scientists at Purdue University in the US created this computer-rendered visualisation of the planes as they hit the buildings. Released in 2007, it was the first to show the structural damage caused to the main support beams with scientific accuracy.
Their research found that it was the weight of the fuel combined with the fire, and not the aircraft itself, that caused the most damage to the buildings. Watch the video below to see compelling imagery of the impact.
The team working on the project hope the visualisation will help develop structures that can withstand such impacts — that could be built around airports where accidental collisions may occur, for example — in the future.