Evidence law is the body of law that deals with how facts must be proved in a legal proceeding. In criminal law, the rules of evidence govern what evidence is admissible or inadmissible in a trial and the procedures the police must follow when obtaining evidence. This includes how suspects are interviewed, how searches are conducted and how forensic evidence is stored and analysed. It also covers how witnesses are questioned during examination-in-chief and cross-examination and who is a competent and compellable witness.
There are strict rules of evidence that apply to how witnesses are dealt with during a criminal proceeding. These include rules about hearsay, opinion evidence, relevance, privilege and identification evidence.
When parties to a criminal proceeding are in dispute about the admissiblity of an item of evidence, a preliminary proceeding called a voir dire may need to be held so that the court can make a ruling as to whether the evidence is to be admitted or excluded. While sometimes a piece of evidence will be clearly admissible or inadmissible, in other situations this may be less clear. It is also possible in some situations, for a court to exercise its discretion to exclude a piece of evidence that would ordinarily be admissible because of the circumstances under which it was obtained.