TSE BONITO, N.M. (AP) — The Navajo Nation says it's angered by a U.S. Justice Department decision not to prosecute a former Winslow, Arizona, officer who fatally shot a 27-year-old Navajo woman.

Navajo Nation Attorney General Ethel Branch said Tuesday the tribe is planning to sue over the matter early next year. The tribe had asked the Justice Department to look into the March 2016 shooting of Loreal Tsingine (SIN'-uh-jin-ee).

Department spokesman Devin O'Malley said Tuesday the evidence thoroughly was reviewed but officials couldn't prove beyond a reasonable doubt that Austin Shipley willfully used excessive force when he shot Tsingine.

Branch says Tsingine's death is an injustice and is part of a system of violence against Native Americans by law enforcement.

Authorities say Tsingine had medical scissors in her hands when Shipley shot her.