The NIA's clean chit to Pakistan in the Pathankot terror attack was a "monumental failure", Congress leader Digvijaya Singh said on Friday, demanding that Prime Minister Narendra Modi should explain "if Pakistan did not have a hand in the attack, then who did"."NIA has given a clean chit to Pakistan in the Pathankot terror attack. Would Narendra Modi and the NSA (National Security Advisor) please tell us, if it was not Pakistan, who were the terrorists who attacked our Pathankot airbase?" Singh asked in Panaji.Terming the development as of monumental failure of diplomacy and internal security handling, Singh demanded: "The Prime Minister and the NSA and Home Minister Rajnath SIngh must come clean on this."The All India Congress Committee general secretary also said that the government did not even know how many terrorists were killed in the attack, citing discrepancy in the figures given by the office of the NSA and the actual dead bodies claimed.