(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."



The body of the then-unidentified toddler was found on October 29. A fisherman found Riley's body stuffed inside a blue storage container that washed up on an uninhabited island in Galveston's West Bay.



A medical examiner said the child's skull was fractured, and a forensic dentist estimated her age at 2 to 3 years.



Police dubbed the child "Baby Grace."  A police artist's sketch of her was widely circulated in the news media and prompted a call to Galveston police from Riley's grandmother in Ohio, who had not seen the girl in months.



On Saturday, police arrested Trenor and Zeigler on charges of injuring a child and tampering with physical evidence, the sheriff's department said. Their bonds were set at $350,000 each.



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 Royce Zeigler, in the physical abuse, death and disposal of the remains of her daughter, Riley Ann Sawyers."



Trenor's statement said on July 24, she and Zeigler both beat the child with leather belts and held her head under water in the bathtub. She said Zeigler picked the girl up by her hair and also threw her across the room, slamming her head into the tile floor.



After her daughter died, Trenor's statement said, she and Zeigler went to a Wal-Mart that night and bought the Sterilite container, a shovel, concrete mix, and other supplies.



The statement said the box containing the child's body was hidden in a storage shed for "one to two months."  Then, Trenor said, she and Zeigler carried it to the Galveston Causeway and tossed it in, and she saw it drifting away.



Riley Ann's father, Robert Sawyers, on Monday tearfully remembered her as a "fun-loving girl ... with a big imagination."  Watch Riley Ann's father describe the little girl »



Riley was "very active, very hyper, but also very well-behaved," Sawyers told reporters in Mentor, Ohio.



She would play "with a water hose ... spraying the whole patio soaking wet until she was done with it," he said, as he sat behind two photographs of his daughter, a toddler with wispy blond curls.



Robert Sawyers' mother, Sheryl Sawyers, said the family was "devastated" to learn that police believe Riley is dead.



"It's hard to think that I'll never see her again," she said, clutching a red Elmo doll she had planned to give Riley for Christmas.



Maj. Ray Tuttoilmondo of the Galveston County Sheriff's Department said Monday that authorities are "fairly confident" that the toddler whose body was found on October 29 is Riley Ann Sawyers.



DNA analysis is still in progress to confirm the identification. The results will be available in two to three weeks, Tuttoilmondo said.



Tuttoilmondo said Riley is originally from Mentor, Ohio, a Cleveland suburb, and that "she and her mother came down to Texas earlier this year."



The toddler was last seen in Texas "three or four months ago," Tuttoilmondo said, although he did not know by whom.



Tuttoilmondo said police did investigate whether Child Protective Services had taken Riley away, something the mother had reportedly alleged
What does the affidavit quote? Who did the mother's husband throw? Who was thrown across the room? Who threw Riley Ann Sawyers across room? Who was arrested? Who attempted suicide? Riley Ann's mother and her husband arrested after a tip led to search
girl's mother, Kimberly Dawn Trenor, described to police how her daughter died and was put in a plastic storage box Riley Ann Sawyers 2-year-old Riley Ann Sawyers Zeigler Trenor and Zeigler Royce Zeigler, police artist's sketch
question: What does the affidavit quote?, answer: girl's mother, Kimberly Dawn Trenor, described to police how her daughter died and was put in a plastic storage box | question: Who did the mother's husband throw?, answer: Riley Ann Sawyers | question: Who was thrown across the room?, answer: 2-year-old Riley Ann Sawyers | question: Who threw Riley Ann Sawyers across room?, answer: Zeigler | question: Who was arrested?, answer: Trenor and Zeigler | question: Who attempted suicide?, answer: Royce Zeigler, | question: Riley Ann's mother and her husband arrested after a tip led to search, answer: police artist's sketch