US investigators said today they have solved one of the mysteries of the 9/11 attacks which has been a long-running source of conspiracy theories – the collapse of World Trade Centre building 7 (WTC 7).

A computer simulation of the 2001 World Trade Centre attacks supports a federal agency’s findings that the initial impact from the hijacked aeroplanes stripped away crucial fireproofing material and that the weakened towers collapsed under their own weight.

US GOVERNMENT investigators said the World Trade Center buildings would probably not have collapsed in the September 11, 2001, terror attacks if fireproofing had stuck firmly to the columns and floors.

US government investigators said the World Trade Centre buildings would probably not have collapsed in the September 11 2001 terror attacks if fireproofing had stuck firmly to the columns and floors.