This investigative report produced by the Dateline programme probes into the role of the Mujahedin-e-Khalq (the MEK) in providing intelligence related to the the Iranian nuclear programme to the US. The MEK is a listed terrorist organisation, which is amongst the world's most equipped and well armed, having under its control a functional military capability. Following the historic and infamous Iraq intelligence failures, this report questions once again the credibility of US intelligence sources.