The Rock of Judgement was an asteroid in the Uva Beta Uva system. The inhabitants of the system built a prison on it, where the worst criminals were brought. There they were tried, convicted and executed.
The Rock itself was fitted with engines, and travelled along a secret course known only to those with clearance. The Rock's security relied heavily upon the difficulty of finding it at all in the vastness of space. (PROSE: The Romance of Crime, AUDIO: The Romance of Crime)