Expert witnesses may give expert evidence on facts based on their expertise. Others may rely on expert witnessesí opinion about a fact in issue within the domain of their expertise as expert opinion for assistance to the fact finder or the concerned Court.
The judge can call upon an expert to technically evaluate a certain assertion of fact for assistance in the act of judging. The opinion of such a court appointed expert may then be tallied with the observations of experts of the parties.
The expert has heavy responsibilities, particularly in criminal trials. Perjury by an expert is a severely punishable offence.
The trial may be stayed for a limited period to enable the concerned expert to study the matter and furnish the results of his inquiry.
A party may hire non testifying expert to help him in appraising his case. This type of expert opinion is not open to discovery or disclosure .Any adverse finding of the expert against his client will never be available to the opposite party to take advantage of.
However, all documents used to prepare the report or testimony of a testifying expert, who will be a witness in court, is liable to disclosure.
The use of party nominated experts in witness action has come under a lot of criticism since such experts are used by both sides to justify their respective positions and it is often left to a jury of layman to decide which expert witness to be trusted.