Let's say there were a man who murdered someone (or maybe raped someone). Let's say he spent about 20 years in jail. Also, let's assume we had something like a cerebroscope using which we could we could read his brain. On reading his brain, it was found that the man truly regretted his actions and he had genuinely changed, i.e. he had been "rehabilitated".
Considering this, would you still want to keep him in jail for what he did 20 years ago or would you give him a chance at life in the outside world?
If there were such a device, much of criminal justice would change. For one thing, the very subjective assessments that the judge and jury make about how "sorry" the criminal appears would be backed up by actual science, which would keep a lot of socially awkward or ugly people from getting screwed and keep a lot of sociopaths and good actors behind bars where they belong.
And yes, I think that this system WOULD have to be used as part of parole/early release hearings. It would almost have to be. Why release someone who is angry and seeking revenge?
Furthermore, I think that the social stigma against ex-cons would be lowered as well. They wouldn't be out unless they had changed.
We could also use it to screen politicians, CEOs, and other influential people before handing them the reins of power.
Pity such a magical device doesn't exist, eh?