In order to understand the aggressive behavior of an adolescent client, a clinical psychologist has carefully investigated the adolescent's home environment, history of social relationships, past and current academic record, and neurological/brain functioning. which research method has the psychologist employed?

The research method that the psychologist employed here is a case study.
A case study refers to research of a person/subject over a long period of time; the research will have to do with their development throughout the years so as to see what brought about the person who stands before us in the present moment. In this case, the psychologist wants to see what happened in the past of this adolescent client in order to determine the cause of his aggression in the present.