(Brian Geraghty): The police commissioner who provides covert support for the investigation while trying to clean up police corruption.
: Dr. Kreizler, an "alienist" (an early psychiatrist), believes a serial killer is at work. He conducts a parallel, covert investigation because the police have wrongfully charged a man just to close the case. [S1E1] The Boy on the Bridge
(Luke Evans): A newspaper illustrator who assists Kreizler in gathering evidence. an "alienist" (an early psychiatrist)