MAC's can put you on pre-pay review or refer you to the ZPIC.
RA's can recoup payments.
ZPIC's Contact patients, conduct investigations refers fraud to the OIG, denies or suspends payments.
OIG has a broad investigative authority, may involve criminal prosecution, can exclude your business from participation in federal programs, may criminally prosecute.
DOJ prosecutes federal charges, imposes fines, works with the FBI, engages in civil litigation.