Those who had first gone to discover whether Nephi had prophesied correctly had been thrown into prison. It is apparent that, at least at this time, there was no requirement for investigation prior to the incarceration of those that supposedly committed the murder.
As many people gathered for the Chief Judge’s funeral, the others who had heard Nephi’s prophecy would have clearly understood that it had come true, and that would have reminded them that they didn’t know where the original five were.
That questioning leads to the opportunity for the five to tell their tale to perhaps a more open trial rather than to just acquiesce to the presumptive conditions that had put them in jail.
They testify that they had come to verify Nephi’s prophecy. That story would have clearly been verified by the larger number of people who had been there at the time. This exonerates the five, but doesn’t end the misunderstandings.