(CNN) -- Before dying, 2-year-old Riley Ann Sawyers was beaten with belts, picked up by her hair, thrown across the room and held under water, according to an affidavit from the Galveston County Sheriff's Office. Police believe 2-year-old Riley Ann Sawyers is "Baby Grace." The affidavit says the girl's mother, Kimberly Dawn Trenor, described to police how her daughter died and was put in a plastic storage box that Trenor and her husband, Royce Zeigler, later dumped into a Galveston waterway. Trenor told police Zeigler tried to commit suicide the weekend before Thanksgiving, and wrote a note that said, "My wife is innocent of the sins that I committed."
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Police affidavit quotes mother's statement about beating that killed girl
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Mother's husband threw Riley Ann Sawyers across room, affidavit says
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Husband later attempted suicide, mother told police
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Riley Ann's mother and her husband arrested after a tip led to search
The affidavit, obtained by CNN, says when police interviewed Trenor on November 23, she "gave a voluntary statement on video with her attorney present in which she describes her involvement, with @placeholder, in the physical abuse, death and disposal of the remains of her daughter, Riley Ann Sawyers."