The five were freed, as it was clear that they were innocent. However, the easiest explanation still could not conceive that Nephi was a prophet. Therefore, his knowledge of the event had to have come from having participated in the event.
In addition to this prophecy of the murdered Chief Judge, Nephi had dared to speak out openly against those powerful men who were in the government. He had accused them of leading the people away from God, and if he were to be declared a prophet, it would make it more difficult for those men to retain power. They were only too happy to bring Nephi before the court.
Where the five had been tossed into prison, to be dealt with at a later time, Nephi is brought forth immediately “that they might accuse him to death.” Standing convicted of murder would not only silence his voice, but discredit him and therefore remove him as a threat to the Gadianton-led government.