I think there could be several possibilities on why a child would engage in feces smearing ... there are too many to mention when googled and I am not an expert! But many, and possibly overlapping/comorbid, possibilities include ODD, autism, physical/sexual abuse, attention deficit, being bullied, encopresis , and so on. Here are some reported by parents/caregivers and I tend to think they have to be evaluated based on the kids age also.
http://www.medhelp.org/posts/Child-Behavior/12-year-old-boy-smearing-poop-/show/585404
All of this seems parallel to reports he seems detached ... but again, could he be autistic or? That would put things in an entirely different light.
I also wonder if a kid would put poo on a personal item of a child because it is somehow associated with why the child got that item or the person who gave it to her. Or if it is just an immature act of a sibling who is not getting as much attention - that doesn't mean he is sexually molesting her or murdered her accidentally or not.
IDK, I'm speculating on opening up the possibilities more than closing them since there is so much unknown?
I'm not sure how many of the poo incidents are validated as being B and, if so, what is the rest of the context.