Since the beginning of this century, more and more scholars have studied criminal psychology, and many psychologists have also joined in the study of criminal psychology. S Floyd, the founder of psychoanalysis, believes that the impulse of sexual instinct is the root cause of crime. He pointed out that human consciousness consists of three parts: ID and superego. Id stands for innate desire and impulse, and acts according to the "happy principle"; Superego represents social moral standards and acts according to the principle of "best"; Self and superego coordinate and act according to the "realistic principle". The occurrence of criminal behavior is due to the weakening of the self's obedience to the superego and the tendency to the id. He also believes that adults commit crimes because of degeneration, which revives children's primitive and immoral sexual impulses in their early years. American psychiatrist W Healy and his wife A F· Bronner have studied juvenile delinquency for many years, and put forward "Emotional Disorder Theory" in 1936. They believe that illegal and criminal acts are "expressions of unsatisfied wishes and desires". When young people's wishes and desires are not satisfied for a long time, profound emotional problems will arise. Long-term dissatisfaction will lead teenagers to seek compensatory satisfaction through crime.
American criminologist E.H. Sutherland put forward the theory of different contact in his book Principles of Criminology 1939. This theory holds that (1) criminal behavior is learned through learning. (2) Criminal behavior is learned in the process of interacting with others. (3) Criminal behavior is mainly learned in groups closely related to individuals. (4) The learning content of criminal behavior includes criminal methods, skills, motives, attitudes and reasons. (5) In the formation of criminal motive and internal driving force, we mainly get the wrong idea from interpersonal communication, that is, crime is better than no crime, so that illegal psychology can overcome law-abiding psychology. (6) The results of criminal learning vary with the frequency, duration, sequence and intensity of contact. In crime-prone areas, because there are many opportunities for contact with criminals, there are bound to be many criminal acts.
K. Schneider, a German psychiatrist, made a detailed analysis of the relationship between various abnormal personalities and criminal behavior in his book Personality of Psychopaths published in 1940. He found that there are mainly the following types of abnormal personality that can easily lead to crime: (1) weak-willed, lacking resistance to external temptations, and easily tempted by outsiders to commit crimes. (2) Emotion-deficient type, such people lack noble feelings such as shame, pity, sympathy, reputation and conscience, and have cold and shameless personality characteristics. (3) explosive, this kind of person is slightly stimulated by the outside world, and will break into a furious rage and attack others by violent means. (4) Excited, this kind of person is easily excited, careless, impatient and prone to disputes with others. (5) self-display, this kind of person has a strong vanity and wants to express himself everywhere, regardless of the occasion and way. (6) Paranoid, this kind of person stubbornly adheres to the wrong views and beliefs that violate social norms and puts them into action. (7) Mood is changeable. This kind of person is moody and unpredictable. (8) Weak type, this kind of person lacks the dignity of personality, can't stand the external pressure, and often gives in to others against his will and does what he knows he shouldn't do. (9) Inferiority type, this kind of person is extremely inferior, denies his own ability and knowledge and experience, and thinks that he can't live like a normal person and can only rely on others or take illegal means to make a living. (10) Melancholy type, this kind of person is unhappy and negative all day, and regards everything as something unfavorable to him, so as to dominate his actions.