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... A security camera recorded the killing, inside the bedroom they shared on July 15 in Humboldt, Tennessee, the county prosecutor said.

The recording shows the older child using bedding to suffocate her cousin as the younger girl slept in the top bunk, Gibson District Attorney Frederick Agee's statement said. After the child died, "the juvenile cleaned up the victim and repositioned her body," Agee said.

A relative told WREG-TV in Memphis that the girls had been arguing over an iPhone after coming from out of town to stay with their grandmother.

The girl was charged with first-degree murder and tampering with evidence after authorities obtained the video on Wednesday. ...