After four years of research, the release of official conclusions left many unsatisfied. Both buildings were designed to survive the impact of a commercial airliner and the fireproofed steel structures should have survived the fires that followed - yet within two hours both towers had collapsed. In addition, video footage of molten metal pouring from the damaged floors and eyewitness reports of explosions before the collapse were not addressed fully, fuelling conspiracies of a government plot to destroy the towers and drag America into a war on terror. Retired chemist Dr Frank Greening agrees that the report is unconvincing. He immediately spots a glaring omission in the official report - the missing evidence - the role of the airplanes themselves in the collapse. According to the official report, the aircraft disintegrated on impact and played no part in the events that followed. As a chemist, Frank Greening cannot believe that the presence of 30 tons of aluminum can be simply dismissed. In Norway, Dr. Greening's work finds support from metallurgist Christian Simensen, who is also unconvinced by the official findings. After 30 years in the metal industry, Christian knows only too well that 30 tons of aluminum alloys in the heart of the fires and under the right conditions could be highly explosive. Together, Christian Simensen and Frank Greening calculate that the aluminum at the heart of the office fires can explain the molten metal seen pouring from the towers and the reported explosions that they believe triggered the catastrophic collapse.