The dialogue is about a mole who would provide them secret information about the inner circle.
– I don't buy it. Didn't you tell me yourself, nobody turns on
al-Qaeda?– The Jordans have worked him for a year, dinners, money. They
convinced him… it's his patriotic duty to turn on al-Qaeda, and
get rich doing it.
(Film: Zero Dark Thirty – United States, 2012)
Best Answer
I haven't seen the film, but from the context I can guess that it means "to betray". "To turn on someone" means "to betray (someone)": "He turned on me" means "He betrayed me" (he was "with" me and now he is "against" me, and thus he "turned" on me).
(Note that this should not be confused with "to turn someone on" which means "to arouse"...)