Having given such a detailed setup, Mormon closes this part of the event quickly. The messengers go, and it is all as Nephi predicts. They return, and he is freed. All of this happens much more quickly than the build up. This is because it is the build up to prophecy that is interesting and important to Mormon. Mormon’s intent in writing is to propose Nephi as a prophet, and so he spends his time on that aspect, not the sham trial for which he already knew the conclusion.