If you are a member of the Guild and in jail... You're probably not low man on the totem pole. I would think something similar to the mobsters in Goodfellas... A nice, relaxing bit of time away from the streets, the wives, the mistresses, and the money.
The whole thing is that prisons... Are a bit different than what you think of. If you are going for a 'modern prison in Eberron' feel you have to think about the needs of the various prisoners. Mages and other casters would probably be kept doped up... In my own setting dissident mages are 'disrobed' through lobotomy, but the wardens may have a fallen member of House Jorasco who is skilled at mixing magic, illness, and drugs to keep the various spellcaster powers in check, along with traditional means (ethereal blocks, dimensional anchors, lead-lined cloaks and helms with tongue depressors to prevent use of powers during mixture with the population).
I think a sort of urbane Druid using the Swift Hunter archetype would provide for an interesting little twist. Sort of Hannibal Lecter type, but more of the charismatic 'handsome killer' Ted Bundy vibe could be useful. He became obsessed with hunting young women of his chosen Favored Enemy type, to the point that he could not be ignored by the inquisitors who tracked him down and dragged him in... But his knowledge of the mind of the criminal caster is useful.
Just remember that, if there are casters, they need to be kept under control. Traditional turnkeys aren't going to be able to keep them down, though it could also lead to a great jailbreak.
What I would do...
Perhaps someone has paid several men to be tattooed in an invisible ink. These prisoners begin dying or disappearing, and their skin serves as a spellbook for an imprisoned mage.
The mage's fellows, knowing that the mage needs to be able to bring himself back to full strength after the draining of his skills, has sent in a skilled Rogue with ranks in UMD. They also sent in his shill, a man who was paid to be pinched... And whose femur has been carved and shaped into a wand of restoration, at great expense.
The Mage has hidden the tattooed skins, and the Rogue knows that the Mage needs the prisoner killed. When given the chance the prisoner will be killed, his femur torn from the corpse, used to Restore the Mage, and then the fun begins

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Slainte,
-Loonook.