The adjective forensic describes scientific methods used to investigate crimes. If you're looking for forensic evidence, you're using your scientific know-how to find proof that will help solve crimes.
The adjective forensic comes from the Latin word forensis, meaning “in open court” or “public.” When you describe something as forensic you usually mean that is has to do with finding evidence to solve a crime. It could also mean that it has to do with the courts or legal system. You could have a forensic advantage — meaning an advantage in court — if the forensic team — meaning the investigators — found no forensic evidence of you being involved.