I've spoken to Skadi on the matter of moles in Svarga. I've informed her we are fond of her, her Glasthein blood important to us and that she still matters. She didn't like the idea of our planting a mole but...ah. I'll copy what she said:
"With me leading this. I choose the mole, reports will be sent to both regions, unaltered and identical. You trust me not to withold information."
I find this acceptable. If we are to be trusted, we must give trust. Whether or not we personally like this doesn't matter. It will develop into a strong bond in the long run, deepening the relationship between the two regions until we have less trouble with them. Skadi, unlike a full-blooded Svargan, would be a good place to start with bonds like this in Svarga as well. We can branch out from her later to others.
I realize your goal is to find the killer but we must also look ahead toward Glastheim's future and not just its past.