Detective Hahn is a tall black man with major physical strength. He has a padlock-shaped facial hair and usually wears a suit. He is John's friend and pretends to be on his side even after John tried to beat him up but it turns out that he has been secretly coveting his wife, Alex.
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Hahn is one of the detectives who are trying to find out who the Ten Commandments Killer is. He is John's friend as well and has always supported him. 
After finding out that he is the killer, John goes to him to confess but he tries to convince him that he is a good person and wouldn't do such thing. Then, John tells him that he knows he wants Alex and stabs him two times in the stomach area.