Canadian Criminal Procedure and Practice/Trials/Calling of Witnesses
Calling Witnesses 
The usual manner that a witness testify is by oral testimony in court (viva voce evidence) while the accused is present. (CCC s.650(1))
The witnesses' testimony must be relevant, material, and admissible. To see details on the scope of these requirements see Canadian Criminal Evidence.
Choice of Witnesses 
Any party is entitled to call a witness who is competent to testify (See Canadian_Criminal_Evidence/Testimonial_evidence for details on competency of witnesses).
A party is also permitted call a witness that has already previously been called by the opposing party.
A party cannot call a witness for the sole purpose of discrediting a witness who has made a previous inconsistent statement.
The failure to call a witness can be used to make an adverse inference where there is no plausible reason not o do so and it is well within the power of the party to do so. However, where the evidence is merely cumulative or inferior en it should not be taken into account. (R. v lapensee 2009 ONCA 646)
A failure to call a witness cannot be used to make a negative inference on credibility of the accused.
- R. v. Cook, (1960), 31 W.W.R. 148 (Alta. S.C.A.D.)
R. v. Baiton, 2001 SKQB 264
R. v. Sutton 2002 NBQB 49
- R v Soobrian 1994 CanLII 8739 (ONCA)
This relates mostly to crowns calling a witness apply under s. 9 CEA to cross examine (see Canadian_Criminal_Procedure_and_Practice/Trials/Examinations#Cross-examining a party's own witness (Adverse or Hostile Witnesses)
- See Canadian_Criminal_Evidence/Credibility#Failure_to_Call_Witnesses
Testimonial Aids 
Witness Screens 
On application by a prosecutor or witness, the judge may order that their testimony be heard either behind a screen or from a different room so that the witness cannot see the accused.
The governing section is 486.2 which states:
Testimony outside court room — witnesses under 18 or who have a disability
486.2 (1) Despite section 650, in any proceedings against an accused, the judge or justice shall, on application of the prosecutor, of a witness who is under the age of eighteen years or of a witness who is able to communicate evidence but may have difficulty doing so by reason of a mental or physical disability, order that the witness testify outside the court room or behind a screen or other device that would allow the witness not to see the accused, unless the judge or justice is of the opinion that the order would interfere with the proper administration of justice.
(2) Despite section 650, in any proceedings against an accused, the judge or justice may, on application of the prosecutor or a witness, order that the witness testify outside the court room or behind a screen or other device that would allow the witness not to see the accused if the judge or justice is of the opinion that the order is necessary to obtain a full and candid account from the witness of the acts complained of.
Video Testimony 
Section 714.1 of the Criminal Code allows a court to use “means of technology” to allow a witness to testify as a “virtual presence”.
714.1 A court may order that a witness in Canada give evidence by means of technology that permits the witness to testify elsewhere in Canada in the virtual presence of the parties and the court, if the court is of the opinion that it would be appropriate in all the circumstances, including
- (a) the location and personal circumstances of the witness;
- (b) the costs that would be incurred if the witness had to be physically present; and
- (c) the nature of the witness’ anticipated evidence.
The purpose of s. 714.1 is to "address not only the high cost of litigation, but also the inconvenience of disruption to the lives of witnesses" where the witnesses are outside of Canada. Consequently, the higher the cost and inconvenience harder it is to resist video link as an option.
There is a presumption that the "unless the circumstances warrant dispensing with the usual practice, the witness should be called to the witness stand to testify." Section 714.1 "does not replace the established procedure of calling witnesses to the witness stand in criminal cases or of allowing the accused to face his or her accuser" 
The court can do "a sort of distance-cost, benefit-prejudice analysis" to decide. Naturally, most applicants have witnesses that are in "more remote regions of Canada."
However, "cost saving to the state,...,in and of itself does not justify" the use of video conferencing.
Factors to consider include:
- 1) will a video appearance by the witness impede or impact negatively on the ability of defence counsel to cross‑examine that witness?
- 2) the nature of the evidence to be introduced from the witness and whether it is non‑controversial and not likely to attract any significant objection from defence counsel, for example various police and technical witnesses who testify to routine matters with respect to exhibits and the like and other matters that would not attract any particular objection on the part of the accused's counsel;
- 3) the integrity of the examination site and the assurance that the witness will be as free from outside influences or interruptions as that person would be in a public courtroom;
- 4) the distance the witness must travel to testify in person and the logistics of arranging for his or her personal appearance;
- 5) the convenience of the witness and to what degree having to attend in person at a distant location may interfere with important aspects of the witness's life, such as his or her employment, personal life and the like;
- 6) the ability of the witness to attend who lives in a country or area that makes it difficult to arrange for travel or travel in a reliable fashion;
- 7) the cost to the state of having the witness attend in person; and
- 8) a fact to consider also is that the witness is effectively beyond the control of the Court in the trial jurisdiction, and whatever powers a judge may have over such a person, they are certainly extraterritorial.
While the form of the order is at the discretion of the judge, the court should always order that witness be able to testify in a manner in which he can be seen, heard, and questioned by the parties. The court may also request the evidence only be given while the witness is in a courtroom and in the presence of a peace officer.
Use of Pseudonyms by Witnesses 
The Court has discretion to allow a witness to testify under a pseudonym only where a failure to do so would interfere with the administration of justice. This includes where the witness has reason to fear for their life.
- R. v. McKinnon, (1982), 39 A.R. 283 (Alta. C.A.);
Attorney-General v. Leveller Magazine Ltd,  1 All E.R. 745 (H.L.)
R. v. McArthur, (1984) 13 C.C.C. (3d) 152 (Ont. H.C.J.)
- R. v. Gingras (1992), 120 A.R. 300 (C.A.)
R. v. Mousseau, 2002 ABQB 210
Every person charged with a crime has a right to the assistance of an interpreter where they cannot understand the English or French language. This right requires that the interpreter be competent as an interpreter.
Interpretation must be continuous, precise, impartial and contemporaneous. 
See: R. v. Wong  O.J. No. 2325
- Canadian Charter of Rights and Freedoms section 14
- R. v. Rybak,  O.J. No. 1715, at paragraph 84
R. v. Sidhu,  O.J. No. 4881
- See R. v. Sidhu, 2005 CanLII 42491 (ON SC), (2005) 203 C.C.C. (3d) 17 at para. 298
- R. v. Tran, 1994 CanLII 56 (SCC), (1994) 92, C.C.C. (3d) 218 (S.C.C.)
- R. v. Wong, 2011 ONCJ 264 at para. 20
Witness Problems and Issues 
Refusal to Testify 
Communicating with witnesses 
Counsel cannot talk to a witness between cross-examination and re-examination without asking for leave of the court. 
- R. v. Montgomery, 1998 CanLII 3014 (BC S.C.)