In this article, we explore the concept of criminal psychology and will explicate some of its major tenets in characterization of Hercule Poirot. Using an interdisciplinary approach, by close reading and drawing from crime and psychological theories (especially Behaviorism), we investigate the criminal profiling techniques in Agatha Christie’s detective novels. Particularly, we adduce Ian Marsh’s theory in introducing a set of explanations for criminal behavior and Westera et al.’s propositions in identifying features that make a detective’s endeavors effective. We focus on the psychological procedures that exist in the process of mystery (making and solution), as well as on the detective’s task to decodify riddles in light of the internal and external forces acting on him and how these affect his final decision. Then, we expand the notion of profiling as conducted by a detective and will illustrate some of the recurring biases that influence the final verdict about a case. Finally, we depict how the abovementioned proceedings are implemented in Murder on the Orient Express (1934), The A.B.C Murders (1936), and Hickory Dickory Dock (1955), three of Christie’s best-selling novels with Hercule Poirot as their leading character. The character of Poirot, with his immaculate criminal profiling, bears witness to how Christie drew from and, at the same time, contributed to the concept and practice of criminal psychology in fiction.