Associated Press
A crowd marches to the Navajo Nation Council Chambers on Wednesday, July 20, 2011 in Window Rock, Ariz., in support of tribal legislation that would criminalize domestic violence on the reservation.

Indian reservations rank among the most violent places in the United States but a good chunk of crimes aren't being prosecuted.

Rape and sexual assault rates among American Indian women are four times the national average, according to the Department of Justice. Women living on reservations are 10 times more likely to be murdered than other Americans.

The Justice Department, though, only files charges in about one third of sexual assault cases and half of murder investigations, the New York Times reported this week. United States attorneys and the Federal Bureau of Investigation have jurisdiction over serious crime in Indian Country.

While tribes worry the low prosecution rate is contributing to the high crime rate, prosecutors argue the majority of reservation cases are turned down because of lack of admissible evidence. Growing tension has pushed some American Indians to sue the government for sloppy police work.

“One of the basic problems is that not only are they declining to prosecute cases, but we are not getting the reason or notification for the declination,” Jerry Gardner of the Tribal Law and Policy Institute in West Hollywood, Calif., told the New York Times. “The federal system takes a long time to make a decision, and when it comes to something like a child sexual assault, the community gets the message that nothing is being done.”

President Barack Obama has called the violent crime rates on reservations "an assault on our national conscience that we can no longer ignore."

The federal government recently wrapped up a two-year crime-fighting initiative at four of the country's most dangerous reservations, the New York Times reported. The initiative, which was modeled after a military strategy used in Iraq in 2007, brought hundreds of federal officers to the reservations. Crime rates dropped on three of the four reservations.

In an effort to repair the justice system in Indian Country, the president also signed the Tribal Law and Order Act of 2010, which increased the authority of Indian police and gave Indian courts the power to issue stronger sentences.