The invasion by the Lamanites was in direct violation of a solemn treaty. The question between kings is therefore the nature of the violation. The oath had to mean something, and therefore there must have been some breach. Upon finding out that there was indeed a breach of the treaty, Limhi declares that he will search his people to find the perpetrators.
Once again in this incident we see a different world at work than the modern one with which we are familiar. Rather than rejoice over a conquered opponent, the issue is not the killing, but the breaking of an oath. When Limhi finds that his own people might have been the ones to break the oath, the entire situation changes. Rather than the triumphant victors, the Limhites are now possibly humiliated with lack of honor. The honor of his people requires that the situation be resolved. We have moved away from the warfare and into a question of integrity.