Speculating, but I think this means they are trying to figure out if Skyler putting the baby in the backyard grave fits the legal definition of abuse of a corpse (whether she did in fact bury the baby has not been disputed). I think this means they don't believe she burned or "tried to cremate" the baby, which MAY also reflect that they are considering whether what she said in the police interrogations (the second one, in particular) was believable--because I think most reasonable people/jurors would agree that burning a baby's body with a lighter is abuse of a corpse.