To address all issues, there are sub branches of forensic psychology that allow you to specialize in your area of interest. First you have to attain the credentials to work as a forensic psychologist and be involved in the fieldwork to know the area you fit best. Clinical-forensic psychology is a subfield that caters for clients who have mental issues and their issues are of importance to legal decision making.
There are cases where the defendants are underage or elderly. In this area developmental psychology is applied to help in policy making. Before the court gives the final decision, there are jurors who listen to the case and arrive at a common decision. Social psychology subfield looks at how these jurors interact and arrive at a unanimous decision. These branches of forensic psychology allow the psychologists to work together with other people from different fields.
Other branches of forensic psychology are cognitive psychology that looks more at how people make decisions in legal cases. Criminal Investigative psychology deals with police psychology, criminal profiling and psychology autopsies. Forensic psychologists are trained to work as a team to come up with lasting solutions. The subfields may be wide but the cases you face are similar or have related backgrounds.