Or they could duel. But, that takes too much time.
In white night Harry strolled in, challenged and a duel was set up almost immediately. But the same rule applies. The murders were not seen as a breach of the accords but as something for which another member of the accords had reason to ask for compensation.
The accords would then offer some framework to settle the dispute. The white council could have chosen to ignore it and then it would not have been an accord matter at all.