The Conspiracy Files investigates whether the Oklahoma City bombing was the work of lone bomber Tim McVeigh, a decorated Gulf War veteran, or whether there were others involved who are being protected in a government cover-up.
The bombing of April 19, 1995, was the biggest attack on American soil before 9/11, killing 168 people, including 19 children.
The programme talks to conspiracy theorists who claim that the US government not only had foreknowledge of the attack, they had informants inside the conspiracy who actively encouraged the bombing.
The film features revealing interviews with the leading FBI investigators in the case, one of whom, for the first time, is now calling for the investigation to be re-opened.
Producers: Ivan O'Mahoney and James Giles
Series Producer: Mike Rudin
Executive Producer: Frank Simmonds