We don't yet know who did it, but at the very least, why did her mother not protect her? This from the article in post 1:
"A doctor’s report, cited in the affidavit, referred to “chronic and acute” injuries found on several parts of her body. Physical examination, which revealed 21 separate injuries, showed Kavannah suffered multiple abrasions, bruises, lacerations and contusions. She also had fractured ribs, traumatic injuries to her internal organs and brain, and was malnourished. “This was an ongoing abuse of this child for several years that was undetected to this point,” Chief Elliott said.
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