Penology, Justice and Liberty

When a person is convicted of a crime what should be done? Should the criminal experience the full wrath of the law (retribution) or be written off as a victim of circumstance, powerless against his/her own biological or psychological tendencies (rehabilitation), or should we focus on the prevention of crime (deterrence) and not the criminal? Because we live in a democracy, whatever policy is employed is done in our name. Do we have a moral and ethical obligation to examine and justify our views on this matter?