Had a thought yesterday that murdered people are more prone to become ghost pokemon, that can potentially expose their murderer.
A murderer might circumvent this loose end by bonding with a ghost pokemon enough that they can track where their spirit will manifest, allowing it to be captured and kept quiet.
The biggest hurdle to this is not only a ghost pokemon’s inherent mischievousness, but that they might find such a criminal distasteful in most circumstances. Unless they are also dark type as well.
Dualed with fairy type, they would be doubly compliant with such a plan.