By Lori Grannis
MISSOULA, Mont (Reuters) - A 3-year-old boy is the lone witness to the murder of three people shot to death by a fellow tribe member on the Crow Indian Reservation in Montana and has identified the suspect, the FBI said in court papers on Thursday.
The FBI affidavit was filed with a federal criminal complaint charging the suspect, Sheldon Bernard Chase, 22, with first-degree murder in Tuesday's slaying of his cousin, her boyfriend and her grandmother.
Chase, described in the affidavit as having "a documented history of mental illness," was arrested on Wednesday in Spokane, Washington, about 500 miles from the scene of the crime, after a manhunt across several Western states.
He made his initial court appearance in Spokane on Thursday and will be returned to Montana by federal marshals to face prosecution there, said Joseph Harrington, the assistant U.S. Attorney for eastern Washington.
Crow officials said all three victims were tribal members, identified by the FBI as Gloria Sarah Goes Ahead Cummins, 80, her granddaughter Levon Driftwood, 21, and Driftwood's boyfriend, Rueben Jefferson, 20. Driftwood was Chase's cousin.
The FBI affidavit said Chase was also "an enrolled member of the Crow tribe" but indicated he had been living with his mother in North Dakota.
If convicted, Chase faces a mandatory sentence of life in prison, Harrington told Reuters. He declined to discuss details of the case.
The FBI affidavit said investigators' interview of the 3-year-old witness indicated that Chase shot Jefferson as the two were fighting, then shot Driftwood and Cummins. All three victims were struck in the face or head, the FBI said.
A second child was home at the time, but the affidavit did not disclose either youngster's relationship to the victims.
The FBI previously has described the murder weapon as a high-powered rifle. The affidavit said Chase took a "Sitting Bull commemorative rifle" with him from his mother's home the day before the triple slayings but did not make clear whether investigators believe that gun was the murder weapon.
The affidavit also said Chase had stopped taking medications prescribed "to him to address his mental health issues."
The shootings occurred at the grandmother's home outside the town of Lodge Grass, a rural community of roughly 500 people about 60 miles southeast of Montana's largest city, Billings, and 20 miles north of the Wyoming border.
The Little Bighorn Battlefield National Monument, where Lieutenant Colonel George Armstrong Custer and his cavalry unit died fighting Indian forces in 1876, lies several miles to the north of Lodge Grass on the reservation.
(Writing by Steve Gorman; Editing by Cynthia Johnston)