For the past 16 months, he had worked as a mole, posing as a militant jihadist in the Islamic State while passing critical information to a secret branch of Iraq’s national intelligence agency. His record was stunning: He had foiled 30 planned vehicle-bomb attacks and 18 suicide bombers, according to Abu Ali al-Basri, the agency’s director. Captain Sudani also gave the agency a direct line to some of the Islamic State’s senior commanders in Mosul.