On the Edge there are many prisons. Some of them are just normal, regular prisons, but you can also find a special prisons.
Heavenworlder (name) is trying to learn about human psychology. Probably the best place to learn about "true human madness" is prison for unstable human murderers.
"He talked about murders with some sort of weird passion. But he started to be aggressive when I asked him about his childhood experiences. He struggle against cuffs and tried to reach me. If not for the guards behind me this would be probably my last day." -- Anon Guest
Walls and bars do not make a prison, but they certainly help. That said, there are many ways to restrain those who are abundantly dangerous and Humanity has been through literally all of them. From outright execution through shipping them off to a distant land with optional deadly hazards, and finishing with... this.
An entire planet dedicated to keeping the homicidally dangerous peaceful, happy, and contained. The population is incredibly sparse, and the landscapes are stocked with animals for them to predate upon. Those who need company have companions who are trained to handle them without making it look like they were being handled. Those who don't are well away from any intelligent life they could harm.
There is a city, but it is populated almost exclusively by the people who study the people who only know murder as a valid response to life's challenges. It is well-fortified. Entrances and exits are tightly controlled. Not that the dangerous residents care very much for city life, but those who choose to live there prefer to feel safe whilst they do so. Many who live there are fellow Humans. Some were Galactics of a tougher breed. One... was not.