As I mention on the forensic psychology careers page, anybody interested in pursuing forensic psychology careers would benefit from studying psychology in general to start with. Many specialist postgraduate courses in forensic psychology will assume that the student has completed a course in general psychology prior to applying.
This makes sense whether you want to pursue forensic psychology as a potential career choice or whether you'd simply like to learn about the topic in greater detail.
A basic understanding of the main perspectives and schools of thought within psychology would allow you to reflect upon their application within a legal context in a much more focussed and theoretically driven manner.