In the Grand Duchy of Nonscrundi ruled by a Magocracy, a character must undergo a Trial by combat.
He has been framed by A cult or brotherhood - bound by a mission and code - and if found guilty of Murder, his punishment will be Trap the Soul. Put the prisoner into a gem. Break the gem when the sentence finishes. Note the gem must have a value based on how powerful the prisoner is, but the type and shape of the gem remains up to you. Perhaps those glowing red gems in the horned demon statue’s eyes have more than just good market value….

Grand Duchy - The dominion of the grand duke, who is higher ranking than the duke, but beneath the archduke. Usually a member of the royal family in line of succession.
Magocracy - Magicians who were credited with great power often became chiefs and kings in early societies. A magocracy is a form of government in which society is ruled by such magi, wizards, or witches. The term is used in the Dungeons & Dragons role-playing game and other works, by analogy with aristocracy, meritocracy, and theocracy.
Trial by combat - Fight to the death, winner is innocent