A difficult choice had to be made and I tend to go with the majority here whose decision was to repel the raiders from Jhelom. I agree that the evidence, such as it is ,appears to implicate Moonglow, however there is no PROOF.
Everything is circumstantial and nothing can be as misleading as circumstantial evidence.
A wizards hat?, if you wanted evidence to point to Moonglow what else?.
Used spell scrolls?, Moonglow is home to skilled mages, would they need scrolls?.
A group dressed like mages?, also a good disguise for people who are not.
Empty potion bottles?, mages are not the only ones able to use these.
Sulfur?, the same applies, others know its use.
It is possible the whole event was staged to implicate Moonglow, it is also possible Moonglow is guilty.
A possible motive for Moonglow?, the only obvious one is to stop the production of arms and armour by
Jhelom. They must know however that Jhelom is already sufficiently equipped for war if required, why incite them to action?.
I wonder if the whole thing might not have been engineered by someone as yet unknown (Koba?) with the sole purpose of furthering the discord within the Kingdom.
Moonglow may well be the villain here but even so unilateral action by another city cannot realistically be condoned. We are a Kingdom of unified cities and if cities begin to go to war without notice or warning the
end is near for all of us. I think we of the Guard must stand together, if and when this happens, to deter others from a similar course.