Adeptus Arbites
They are basically the police of the Imperium. But they aren't just any ol' cops, they are badass motherfuckers, kinda like robocop but human. They usually drag the criminal up to the judge who then ceremonially declares them guilty and being guilty means that you have committed a crime. And in the Imperium there is only one crime and it is HERESY!!!!!!! On some worlds though, they send the criminals into the penal legions instead of executing them on the spot, thus they may receive the Emperor's benediction on the glorious field of battle. The adeptus arbites have slightly smaller balls of steel than guardsmen, they are on the other hand made of much more man sauce than SPESS MEHREENS and their sissy power armor. An example of this would be the well known quote "Armor? Guns? HAH! Who needs 'em? I just got mah fists and mah club. Now lets go and arrest those two ogryn who have been cauzin' trouble." - Jormund Wilkfas Arbites Sergeant of the third detachment on Necromunda