Welcome attempt at a mundane murder mystery. However it seems to concentrate on the wrong sort of information and has some bizarre restrictions. Why would investigators not be allowed to break a lock to enter a room where the murder was done, or to cast divination spells? (For sure, a court should insist on hard evidence, otherwise an illusionist could run riot.) A list of statements from the suspects would be more helpful than their statistics. There is some confusion about the murderer's motive: is it jealousy, as in the Synopsis, or to protect another, as hinted at in the Conclusion. Some of the clues are good: pack with clothing in the Hay Loft, fine quality but old clothes of the victim. Fragments of letters turning up in strange locations is not so good: why not have these as readable remains of the burnt letters in the fireplace?
I would make the PCs members of the watch on patrol. With rewrites, this could be a good adventure.