For a county that has long stood beneath a legal cone of silence when it came to police shootings, and enjoyed the relative absence of media scrutiny that is focused on cities but not suburbs, Fairfax County is on the verge of a historic, 180-degree change of direction. It is poised to hire a full-time independent auditor who will “participate in and monitor all Internal Affairs investigations” of police shootings, in-custody deaths and all other police-involved deaths or serious injuries, the Fairfax Board of Supervisors indicated in a hearing Tuesday.