Detective Arnold John Flass was a member of the Gotham City Police Department. Heavily corrupt, he was ordered by then-commissioner Gillian Loeb to attack captain James Gordon, who had a reputation for being one of the very few honest cops in Gotham City. This attack failed, and Loeb and Black Mask were forced to try different tactics in order to get Gordon under control.
Flass was also known to steal contraband, and other equally corrupt officers had no qualms about reporting him for their own gain.
- As with commissioner Loeb and lieutenant Branden, Flass was borrowed from the graphic novel Batman: Year One by Frank Miller, which served as a major influence for Batman: Arkham Origins.