So, last session, the party I GM for came into possession of a rod of wonder, without knowing what it was. The INT 8 bloodrager was looking at it, pushed the button, and fireballed a flower stand across the street, destroying some property and singing an old woman, but no one was killed.

The party was arrested, and are currently in temporary holding while they are being interrogated. The guilty party member has confessed to his mistakes, and the rest of the party has defended him but also told the guard that it was him that activated the item.

What should be an appropriate legal punishment? Should there just be a fine, incarceration for just the guilty party member, incarceration for everybody, etc? The players are understanding if characters get lost, but I'm not sure what this incident would warrant.

The incident went down in one of the world's largest cities, but one that's stretched a little thin in terms of resources and manpower.