SIOUX FALLS, S.D. (AP) – An 87-year-old woman suspected of being involved but never charged in the 1975 killing of a fellow American Indian Movement activist in South Dakota has died in a western Nebraska nursing home, a funeral home said Tuesday.

Theda Clarke, an Oglala Sioux Tribe member, had been suffering from the effects of a stroke, dementia, diabetes and other ailments, according to court records. She passed away Saturday, according to the Sioux Funeral Home.

Prosecutors said Clarke repeatedly refused to cooperate as they investigated the death of 30-year-old Annie Mae Pictou Aquash, who was fatally shot and left in a ravine on western South Dakota's Pine Ridge Indian Reservation. The case tainted the legacy of the American Indian Movement, and it was nearly three decades before criminal charges were filed.

Investigators alleged that Clarke, John Graham and Arlo Looking Cloud drove Aquash in Clarke's Ford Pinto from Denver to Rapid City, where Aquash was held against her will and questioned about whether she was a government informant.

In December, Clarke was ruled competent to testify in Graham's murder trial and briefly spoke about her background when jurors weren't in the courtroom. But she exercised her Fifth Amendment right not to incriminate herself in front of the jury and refused immunity, prosecutors said.

Graham, the accused gunman, was convicted of murder, while Looking Cloud was convicted in 2004. Both are serving prison sentences. Clarke refused to talk about the case with an Associated Press reporter in February 2003, two months before Looking Cloud was arrested.

Clarke graduated from St. Francis Indian School in the early 1940s, then began a nursing career at St. Mary's School for Nursing in Kansas City. She later worked on the Pine Ridge Indian Reservation.

She is survived by a son, Edward "Chip" Clarke, of Gillette, Wyo.; a brother, John Nelson of Portland, Ore.; and two sisters, Norma Williams of Denver and Vivian Locust of Pine Ridge. Her family members couldn't immediately be reached for comment Tuesday.

A 3 p.m. Wednesday wake service and a 10 a.m. Thursday funeral service are planned at the Brother Rene Hall in Pine Ridge, with burial at Crawford City Cemetery, Crawford, Neb., said Michael Selzler of Sioux Funeral Home.

The American Indian Movement was founded in the late 1960s to protest the U.S. government's treatment of American Indians and demand that the government honor its treaties with the tribes. AIM grabbed national headlines in 1973, when activists took over the Pine Ridge reservation village of Wounded Knee, leading to a 71-day standoff with federal agents that included the exchange of gunfire.