Answer:
Psychologists in the legal system have a very important role. They may be specialized with scientific knowledge dedicated to research, or some with more basic knowledge.
Psychologists with basic knowledge are the ones who give the legal system details about the functioning of memory, human cognition and social power.
While the best trained psychologists are dedicated to more specific problems in the field of psychology and law, such as the analysis of gestures and behaviors of a suspect during an interrogation.