On the morning of September 11th, 2001, Czech-born architect Jiří Boudník was working on a new federal courthouse in Brooklyn, three subway stops from the World Trade Center in lower Manhattan. After a second airplane hit the Twin Towers, and orders came to evacuate his worksite, Jiří Boudník headed towards Ground Zero, knowing – thanks to his background in civil engineering and architecture and having experienced the 1993 terrorist bombing there – that at least a partial collapse of the Twin Towers was imminent. In the days to come, while organising a volunteer “bucket brigade” to clear debris and retrieve human remains, he developed computer 3D and 4D models of the disaster site that helped firefighters and others safely carry out their grim task.