A nun has been found dead in her residence at a church in a small community on the Navajo Indian reservation near the Arizona-New Mexico border.
Sister Marguerite Bartz, 64, failed to show up at Sunday Mass and a colleague who went to check on her discovered her body.
Investigators believe Ms Bartz was killed between Saturday night and Sunday morning, but the FBI has not disclosed any details about how she died.
Authorities and officials with the Diocese of Gallup, which oversees the parish in Navajo, said they were not sure whether Ms Bartz or the church were the target, or if the attack was a random act.
Ms Bartz was one of more than a dozen Sisters of the Blessed Sacrament ministering within the Diocese, which spans 55,000 square miles (142,450 square kilometres) in New Mexico and Arizona.
The diocese said there is usually another sister who lives at the residence with Ms Bartz, but she was out of the state at a meeting and the victim was alone.