I had this nifty idea for a cleric I made.
He was originally a drug addict who, while under the influence, attempted to rob a shop so he could buy more drugs. He ends up robbing a store in the middle of a real robbery. The arbites come, there's a shoot out. He escapes on his motor bike while the rest of the other criminals die.
The arbites believe him the mastermind and put up wanted posters for his arrest. He becomes infamous, and attracts the attention of a local motor gang.
After some fast talking, they decide not to kill him and he joins their gang. A year or so passes as he tries to get more drugs whilst not getting shot. His time spent with the gang is sort of like Ciaphas Cain, but where he gains infamy.
Eventually he gets caught at the end of a horrible vehical chase. During the chase, he prays to the emperor that if he spare him he'll repent for all the crap he's caused.
In exchange for not excuting him, or sending him to a penal colony, he cuts a deal; He'll use his fast talkin' ways, and connections to help bring down some of the local big time crime syndicates. In exchange he'll live out his sentance in the ecclesiarchies watch.
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Would they allow this? A criminal to enter the holy halls and become one of them after repenting for what he's done? This could also be another way of penance.
He eventually became one of those clerics that whips themselves. If that helps.