Significantly fewer declinations than some have asserted — namely, the 80 percent figure.
GAO Report “U.S. Department of Justice Declinations of Indian Country Criminal Matters”:
From Indianz:
Federal prosecutors turn down 50 percent of cases in Indian Country, the Government Accountability Office reported.
Between fiscal years 2005 through 2009, 10,000 cases were referred to U.S. Attorney’s Offices. Federal prosecutors resolved 9,000 cases by either filing for prosecution, declining to prosecute or administratively closing the matter.
Of the 9,000 cases, only 50 percent resulted in prosecution. In 2005, the declination rate was as high as 58 percent.
“Declination rates tended to be higher for violent crimes, which were declined 52 percent of the time, than for nonviolent crimes, which were declined 40 percent of the time,” the report said.
The declination rate for sexual abuse offenses was even higher — 67 percent. “USAO officials told us that the difference in declination rates between sexual abuse and assault matters may be the result of the difficulty in obtaining evidence and witnesses in sexual abuse investigations,” the report said.
The new Tribal Law and Order Act requires the Department of Justice to provide reports on the declination rates in Indian Country.
Get the Story:
GAO: Feds decline half of Indian Country cases (AP 12/13)
GAO Report “U.S. Department of Justice Declinations of Indian Country Criminal Matters”:
Turtle Talk 
It’s also important to remember that the vast majority of interpersonal violent crime (esp. crimes against women and children) are never reported to law enforcement.