Criminal psychology is the study of the thoughts and behavior of criminals. It answers the question: why do criminals do what they do?

What Does a Criminal Psychologist Do?
Profiling
Yes, criminal psychologists can be profilers, helping agencies create a psychological profile to help apprehend suspects. Unlike what you see on TV, however, a psychologist is unlikely to go with police to confront suspects and a high profile serial murderer only comes along once in a blue moon. Although a criminal psychologist may visit a crime scene, they are more likely to spend time in an office with case files or in a record room poring over analyses of possible suspects. A large part of criminal psychology is looking over research and data relevant to cases. It can almost feel academic. Further, criminal profiling is only one possible aspect of their many duties.
Consultation
Criminal psychologists will often use their expertise to consult with law enforcement personnel on various aspects of a case. For example, they can help them ask appropriate questions during interrogation or give relevant information to help guide their investigation.
Assessment
Assessment is another critical aspect of criminal psychology. Performing psychological testing to determine a suspect’s state of mind is an integral part of the adjudication process. For instance, a psychologist may have to determine whether a suspect is in a stable mental state to stand trial or if they have the personality characteristics to fit the alleged crime.
Research
Criminal psychologists may conduct research that has far-reaching practical implications on the study of criminology and the legal process. For example, psychologists have performed research on memory, eyewitness testimony, evidence collection, and confessions that have impacted how law enforcement professionals and lawyers proceed in criminal legal cases.
Court Testimony
Criminal psychologists often have to appear in court to provide expert witness testimony. There are psychologists whose entire practice is based on giving their expert opinion. They base their judgments on testing they have conducted or through analyzing assessments and evidence provided by other professionals.
Psychotherapy
A criminal psychologist may also be asked to provide psychotherapy for people that have committed crimes. Their role is to help their clients cope with the consequences of criminal behavior and assist them in their rehabilitation so they can be productive members of society.
Teaching
A criminal psychologist can teach at the college level within psychology or criminal justice department. Further, they can teach courses or present seminars at law enforcement training facilities, such as those run by a federal agency (e.g., the DEA) or the police.
How Does One Become a Criminal Psychologist?
First, you need to obtain an undergraduate degree, preferably in psychology. Next, you need to seek a graduate education. A minimum undergraduate GPA over 3.0 ( and likely much higher) is probably needed to gain entry to a graduate program. Please note that criminal psychology is not recognized as an area of specialization by the American Psychological Association (APA). That means you are not going to be able to receive an APA approved graduate degree in criminal psychology. However, you can receive an APA approved degree in forensic psychology. If you do not enter a forensic psychology program, it is recommended that you get a degree in clinical psychology and then specialize in criminology or forensics. Although you can find work with a master’s degree, finding a job as a criminal psychologist usually requires a doctorate.
Hope the above-mentioned information helps in giving some clarity on the roles of a Criminal Psychologist.