Police in Mitchell, South Dakota, said Thursday they were investigating a couple who traveled from Washington state with the body of a dead eight-year-old girl.

The police department said in a statement the couple had driven a U-haul trailer with a coffin containing the body of the girl, who had been adopted by the woman arrested. The couple had informed the Davison County Coroner that they were traveling from Washington state to Pine Ridge, according to the Mitchell Police Department.

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A Washington couple were arrested in South Dakota after the body of an 8-year-old girl was found in their trunk.

The department said the man and woman had told investigators that the girl died earlier in the fall, but gave different dates, South Dakota Public Broadcasting reported. The man arrested told investigators that they had not told authorities about the death because they wanted to spend more time with the girl and were concerned they would "get in trouble."

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The Mitchell Police Department said both were charged with failing to notify law enforcement of the death of a child and the investigation is ongoing.

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The Davison County Jail confirmed that the man and woman were being held. It was not clear whether they had legal representation.