Does doubt about causing an infant's death—by something falling on him or by him falling—necessitate expiation for killing, given the lack of certainty that this occurred?

If it is confirmed that the cause of the child's death was the mother's negligence in placing him next to his sibling or placing part of her body on him during sleep, then she is liable for the diyah (blood money) for accidental killing, which is paid by the aqilah (male relatives on the father's side), and the mother inherits nothing from it. She is also obliged to perform expiation (kaffarah), which is freeing a believing slave; if she cannot find one, then fasting for two consecutive months. There is no sin upon the mother, as the act was an unintentional mistake, and the determination of the cause of death rests with the doctors. If it is not proven that the mother caused or was negligent in the death, then there is nothing upon her.