Section 705 of the Criminal Code establishes and governs the court’s power to issue a material witness warrant to arrest an individual who has been properly served with a subpoena but does not attend court.
In accordance with this provision, the trial judge has discretion to issue a material witness warrant if two pre-conditions have been satisfied: first, that subpoenas have been properly served on the prospective witnesses, and second, that the person is likely to give material evidence.
The decision to grant or refuse a material witness warrant is an exercise of the trial judge’s discretion that should not be lightly overturned by an appellate court. It is a question of mixed fact and law.
Is the person for whom the warrant is sought “likely to give material evidence”?
Where counsel makes little or no attempt to demonstrate that a witness’s testimony will be material, it is obvious that courts should not issue a material witness warrant.
The Supreme Court of Canada in R. v. Scott, 1990 CanLII 27 (SCC),  3 S.C.R. 979 (while considering section 698 of the Criminal Code, which is similar to section 705 but which deals with circumstances wherein a person is not likely to appear in response to a subpoena) noted the following:
While the Court must be convinced that a witness is likely to provide material evidence, counsel does not need to prove that a witness will testify as anticipated. The standard is one of a balance of probabilities
The justice may choose not to insist upon evidence on oath but he may want to conduct an oral examination, if only a cursory one, of some person who has knowledge of the circumstances. The extent of such an examination will depend on the circumstances of each situation.
Courts must balance individual freedoms against the needs of justice and the justice system, aware of the fact that these applications are almost invariably heard without response from those whose liberties are directly affected.