Editing Expert witness (section)

=== Rules of evidence and code of procedure ===

==== Hearsay rule ====
One important rule that applies to the expert witness but not the percipient witness is the exception to the hearsay rule. A percipient witness tells only what he/she actually knows about a case and nothing more. Percipient witnesses cannot give opinions nor conjecture regarding a hypothetical set of conditions.<ref name=":1" /> Conversely, the court does allow an expert to testify about issues that may not be personally known by them. This allows the expert to rely upon scientific articles, discussions with colleagues on the subject, testimony read in preparation for testimony in the case and similar pieces of information not personally known to the expert.

==== Chain of custody ====
{{main|Chain of custody}}
It is important that expert witnesses who handle evidence maintain a proper [[chain of custody]] such that they are able to authenticate the evidence, prove that it is what they represent it to be, when testifying at trial. Most notably in the context of a criminal prosecution, an expert witness who evaluates or examines an item pertinent to an investigation or case evaluation may add an entry to a "chain of custody" document,<ref name=":1" /> a form that contains the item's description, the time and date of release for all prior custodians of the item, and the time and date of release to the witness.

==== Weight of testimony ====
In the case of an expert witness, the weight of his/her evidence depends heavily on the foundation support established prior to an opinion being given. Examples include educational background, review of scholarly works, field studies and trainings which all lead up to developing a foundation of knowledge for credibility of a testimony. Before trial, all experts must prepare a report summarizing their analysis and conclusions and share the report with all other parties.<ref name=":1" /> This allows other parties to effectively cross-examine the expert.