Fun fact, Arbites are more like space IRS/FBI while Inquisitors are space detectives/CIA. Arbitrators are also trained to a very high standard, better than the average planetary defense force or even Imperial Guard grunt (despite how easily they die on the tabletop, Imperial Guard are the equivalent of GIs while PDF troops are National Guard).

The very best Arbitrators are promoted to Judges, who have all the legal powers of Judge Dredd and more.