The entire state police force is now under investigation, with an internal audit linking 21 current and former troopers to overtime abuse in 2016 expanded into a department-wide probe, and Attorney General Maura Healey pursuing potential criminal charges.Massachusetts State Police Col. Kerry A. Gilpin announced the stunning development yesterday, saying she was “disheartened” and has expanded the probe to include the entire department in order to regain the trust of the public.