At least one in three Indigenous women is raped or otherwise subjected to sexual violence during her lifetime, according to the 113-page report, the latest in a series produced by the London-based group’s Campaign to Stop Violence Against Women.

At least 86 percent of reported rapes or other sexual assaults against Indigenous women are committed by non-Indian men who are rarely prosecuted or punished, according to the report, “Maze of Injustice: The Failure to Protect Indigenous Women from Sexual Violence in the USA.”

The failure to pursue justice in such cases is due to a number of factors, the report noted, including chronic under-funding of police and health services, and a “complex maze of tribal, state and federal jurisdictions that is so confusing that it often allows perpetrators to evade justice entirely.”

“What this amounts to is a travesty of justice for the tens of thousands of Indigenous survivors of rape,” said Larry Cox, executive director of Amnesty’s U.S. section.

“Violence against women is not only a criminal or social issue—it is also a human rights abuse,” he added. “In failing to ensure that Indigenous women are protected from violence, the U.S. government is complicit in violating their human rights. It is disgraceful that such abuse even exists today.”

Registered Native Americans, who make up about 1.4 percent of the 300 million total U.S. citizens, are distributed among some 560 tribal governments across the country.

While these governments are given substantial autonomy over their internal affairs, the federal government has steadily eroded their authority, including their justice systems, particularly in areas that involve non-Native individuals or interests.

In one of the most far-reaching cases, the Supreme Court ruled in 1978 that tribal governments cannot prosecute criminal defendants who are non-Indian even if the crime of which they are accused takes place on tribal lands.

In addition, tribal authorities, many of whose communities suffer the highest poverty rates in the U.S., are chronically under-financed, leading to major gaps in law enforcement and the availability of social and health services as compared to non-Native communities.

The report, which was based on Justice Department data and research in three states with proportionately large Native American populations—Alaska, South Dakota, and Oklahoma—found Indigenous girls and women suffered most from these deficiencies.

“American Indian and Alaska Native women are living in a virtual war zone, where rape, abuse and murder are commonplace and sexual predators prey with impunity,” said Sarah Deer, an attorney at the California-based Tribal Law and Policy Institute.

“In many tribal communities, rape and molestation are so common that young women fully expect that they will be victims of sexual violence at some point,” she noted, adding that the weakening of tribal justice systems by the federal government has made it far more difficult for victims of sexual violence to gain redress.

Indeed, federal and tribal statistics may understate the degree of violence suffered by Native American women, according to the report, which noted that fear of retaliation and the lack of confidence that the authorities will take allegations of assault significantly reduce reporting of sexual assault throughout the United States, as well as in Native American communities.

One support worker in Oklahoma, for example, told Amnesty International that only three of her 77 active cases of sexual and domestic violence had been reported to the police.

And many women interviewed on the Standing Rock Sioux Reservation in South Dakota said they could not think of a single Native American woman within the community who had not been subjected to sexual violence at some point in their lives, and that many had suffered several assaults, by different perpetrators.

Native American women were victims in nearly 80 percent of confirmed cases of rape and murder in Alaska over the last 15 years, according to a medical professional responsible for post-mortem examinations of such cases in the state. Native Americans make up only 16 percent of Alaska’s total population of about 675,000.

Jurisdictional issues have often been a major obstacle to successful prosecution of sexual assaults, particularly in states such as Oklahoma, where land owned by nearly 40 different tribes adjoin each other and are often intersected by state land in a “checkerboard” pattern.

Renee Brewer, family violence coordinator with the Citizen Potawatomi Nation in Oklahoma, cited one case in which the victim, a member of the Shawnee Tribe, lived in tribal housing owned by another tribe, the Sac & Fox Nation, but located within the limits of an incorporated city outside of tribal lands.

She had a valid protective order against her estranged husband, a Seminole, who entered her home, beat and raped her, and then refused to leave. When she called 911, police officers from four different jurisdictions showed up.

“Being an Indian woman rape victim in the state of Oklahoma usually means that law enforcement officers spend as much time trying to determine the appropriate responding authority as they do in protecting you from the rapist,” she said.

In that case, police assistance was at least available. In South Dakota’s Standing Rock Reservation, an area of almost 2.3 million acres, tribal police have at most three patrol officers on duty during the day. Nevertheless, Amnesty found that women on the reservation who report sexual violence often have to wait for hours, even days, before receiving a response from the police department, if they receive any at all.

In Alaska, the situation for Native American women in rural districts, a third of which have no police presence at all, is even more dramatic.

In addition to under-funding Native law enforcement agencies, the federal government has also denied adequate resources to the Indian Health Service, according to Amnesty, which found that in cases where health facilities were relatively close and accessible, they often lacked qualified staff or even inexpensive rape kits that would be helpful to any eventual prosecution.

The fact that non-Native perpetrators cannot be tried in tribal courts has actually drawn sexual predators to tribal areas to assault women, because they know that federal prosecutions are rare in those areas, Deer said.

“The majority of rape cases on tribal lands that are referred to the federal courts are reportedly never brought to trial,” Mr. Cox from Amnesty said.

“Sex offenders and predators are well aware of the jurisdictional gaps and confusion created by the Oklahoma checkerboards,” Ms. Brewer added. “Non-Indians often flaunt their crimes because it is so rare that they will be held accountable.”