The rise of the Islamic State of Iraq and the Levant (Isis) has been aided by the continuing failure of the US Government to investigate the role of Saudi Arabia in the 9/11 attacks and its support of jihadi movements such as al-Qaeda in the years since, says former Senator Bob Graham, the co-chairman of the official inquiry into 9/11. Senator Graham, who chaired the Senate Intelligence Committee, said that successive administrations in Washington had turned a blind eye to Saudi support for Sunni extremists. He added: I believe that the failure to shine a full light on Saudi actions and particularly its involvement in 9/11 has contributed to the Saudi ability to continue to engage in actions that are damaging to the US - and in particular their support for Isis." Senator Graham does not suggest that the Saudis are directly running Isis, but that their support for Sunni extremists in Iraq and Syria opened the door to jihadis including Isis. Similar points were made by Sir Richard Dearlove, the former head of the British Secret Intelligence Service, and MI6, who said ... that rulers of the Kingdom tended to oppose jihadis at home as enemies of the House of Saud, but promote them abroad in the interests of Saudi foreign policy. The US and other Western governments have yet to explain why their "war on terror" has so demonstrably failed with the rise of Isis, but tolerance of Saudi complicity in 9/11 will surely be part of the answer.