As I understand, the CIA has not used human espionage agents handled by agency persons for many years, possibly back as far as the infamous Senate Intelligence Committee headed by Senator Church.
They have instead used electronic and now cyber methods (phone taps, listening devises, etc.)Probably their most reliable information has been from friendly foreign intelligence agencies (mostly Britain, France and Italy). (IMO).
Humint is a key element.
Brennan and the rest are leaving Humint ghost cookies for folks to trail.