According to the NIMH, as many as 7.3% of the adult population of the US suffers from a psychiatric condition known as Intermittent Explosive Disorder (IED). These individuals have episodes of uncontrolled rage and aggression which may lead to property damage and violence against self or others. These aggressive impulses are far out of proportion to any provocation, and often quite naturally land the person with the condition in jail. Since such individuals often feel remorse and humiliation soon after an incident of rage, they would seem to be ideal candidates for rehabilitation using techniques developed by psychiatry and neuroscience.
Several treatments have been developed for this condition, of which the most common are cognitive behavioral therapy, mood stabilizing drugs, and antidepressants.  Recently, the use of neurofeedback has been proposed to train people with poor impulse control to resist undesired impulses. One serious challenge with all such treatments is figuring out when someone with the condition has been stabilized or "cured." Parole boards have a duty to the public to ensure that a prisoner diagnosed with the condition is now safe to be released. A prisoner could look sane and stable for quite some time, and then snap when placed in the wrong environment or situation.
I propose that such prisoners could be tested by placing them in a very difficult situation for an extended period of time. Prisoners who can demonstrate their ability to control their temper under extreme circumstances logically should be safe when interacting with the general public, perhaps even more so than the average citizen.
Such tests of stability could take a number of forms. The simplest would be to house the prisoner with a group of other prisoners known to be unpleasant, irritating, and threatening. This would have to be done under very carefully controlled conditions to ensure the safety of the participants. Variations on this strategy could involve the use of actors or plants who pretended to be fellow prisoners in order to test the inmate's response to provocative situations. This strategy is analogous the military's use of "aggressor squadrons" to test how fighter pilots react to hostile situations.
An even more extreme test would be to expose the inmate to low levels of drugs that actually promote anger and compromise executive functioning. Such a strategy would serve two purposes: first, if the drugs are chosen correctly, the prisoner's neurology should adapt over time to compensate, thus causing him to be even more stable once the drugs are removed. Second, prisoners who can control themselves even when their brains have been compromised should logically be less likely to snap when they've been drinking or using drugs, a probable occurrence after release.
 DSM IV, referenced through BehaveNet: http://behavenet.com/intermittent-explosive-disorder
 "Incognito", by Dr. David Eagleman, page 277.