"Who judges the Judges?"
The Special Judicial Squad (SJS) is the Internal Affairs unit of the Justice Department. They are the Judges that judge the Judges. SJS investigates allegations of corruption, unjudicial conduct and criminal activity within the ranks of the Mega-City Judges
Even Dredd has come under suspicion by them in the past. Some hound Dredd for his disregard for the chain of command and tendency to use his own judgement in important situations that affect the whole Justice Department. Others think that a judge that seems as incorruptible and as dedicated as Dredd must be too good to be true.
Their helmets and lawmasters have a skull badge on them and they wear special belt-buckles that have "SJS" instead of the Judge Shield. Their uniform is black rather than Blue or Navy-Blue.