MEXICO CITY -- Authorities in southern Oaxaca state said Saturday they have arrested a man who allegedly raped and killed a U.S. woman.

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Omar Yoguez Singu, 32, told police he had consensual sex with Marcella Grace Eiler, 20, of Eugene, Ore., and then killed her with a machete after an argument on Sept. 15, Oaxaca State Attorney General Evencio Ramirez said.

Eiler's badly decomposed body was found Wednesday in a shack 80 miles south of Oaxaca City, near the town of San Jose del Pacifico.

Ramirez said Singu was turned over to police on Wednesday in Mexico City by friends who first beat him up after he confessed to the crime.

Eiler's father, John Eiler, of St. Louis, Missouri, said his daughter was a dance teacher and social activist in Oaxaca City, where she had lived on and off for the past three years.

"She was really trying to spend her energy as an observer for an indigenous rights organization," John Eiler said in a telephone interview.

Eiler had traveled to San Jose del Pacifico to dance at a fundraiser, said Miguel Cruz of Oaxaca's Popular Indigenous Council, an organization with which he said Eiler had worked since 2007.

She also had lived for about a month with the family of a witness in the killing of Bradley Roland Will, a volunteer for Indymedia.org, Cruz said. Will was fatally shot in October 2006 in Oaxaca City while filming protests by activists demanding the ouster of the state's governor.

Will's family said last year that they believed state officials were probably involved in his killing. State investigators arrested two town officials in 2006 but later released them after then-state Attorney General Lizbeth Cana suggested Will may have been shot by a protester.

Cruz said Eiler had complained that police in civilian clothes often sat in a parked car outside the witness's family's house and that they followed her.

Calls to Oaxaca's state police department were not answered Saturday.

"We're asking authorities to conduct an efficient and transparent investigation and that they not taint her image because she dedicated herself to defending the rights of women and of indigenous people," Cruz said in a telephone interview.

John Eiler said his daughter's remains would be cremated and returned to the United States