Synopsis Criminal psychology is the study of the wills, thoughts, intentions and reactions of criminals. The study goes deeply into what makes someone commit crime, on the run or in court. Criminal psychologists are often called up as witnesses in court cases to help the jury understand the mind of the criminal. The subject-matter will be drawn on the one hand, from that already presented by psychological science, but will be treated throughout from the point of view of the criminal judge, and on this the principles of psychology will be brought to bear.