system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] What does the judicial system consist of in the Imperium? How are prisoners treated?

I know they have penal battalions but besides that I don't know what being an inmate in a prison in the Imperium consists of.
gpt
>I don't know what being an inmate in a prison in the Imperium consists of.

There aren't that many. Keeping prisoners requires resources, and frankly, those are better spent on law abiding citizens. In most cases, you're either powerful enough to get off scott free (Governors, nobility, high ranking administrators etc) loaded into a Penal legion, or executed. A few (and this being the Imperium, we're still talking millions) that are of able body but unfit for Penal Legions can also be given to the Mechanicus, who turn them into Servitors. 

The only individuals you tend to see in any sort of incarceration facility are valued for their information, or slated for other things (the Blacks Arks being massive prison ships for transporting psykers). And neither have pleasant existences. The former are regularly tortured, probed to mind-scoured, and the latter are locked in heavily warded sensory deprivation cells and overseen by psychic nulls.