One final addendum is that we have as of right now no guarantee that the necromancer or non-corporeal entity that has reanimated said deceased person is not somehow capable of either altering the witness or unduly influencing the responses of said witness.
Therefore, the person or being responsible for said reanimation has to first pass muster as to their partiality on the case.
If they can't do that then you can't verify that the witness is giving truthful testimony beyond a reasonable shadow of a doubt