BBC.co.uk | New video has emerged of the 11 September 2001 attacks on New York's World Trade Center, shot by a police helicopter crew hoping in vain to rescue trapped office workers. The video shows the aircraft hovering near the towers' roofs, only to retreat as the first tower fell. "The whole tower, it's gone," an officer is heard yelling. "They knocked the whole fricking thing down." It was released by a US government agency that investigated the collapse. The airspace over the towers was closed to news helicopters on the morning of the attacks, so little video of the attacks from the air has emerged.