Witness
A witness in a criminal trial is a person who testifies under oath or affirmation about facts relevant to the case. Witnesses are called by either the Crown or the defence and are subject to examination-in-chief by the party calling them and cross-examination by the other side. Witnesses are central to virtually every contested criminal trial — the trier of fact decides what to believe based largely on the witnesses' testimony.
Types of witnesses
Several categories of witness appear in criminal trials: (1) Lay witnesses — ordinary persons who saw, heard, or otherwise have direct knowledge of relevant facts (eyewitnesses, neighbours, friends, victims). (2) Police witnesses — officers testifying about their investigation, observations, and dealings with the accused. (3) Expert witnesses — qualified by the court to give opinion evidence within their area of expertise (forensic pathologists, drug recognition experts, accident reconstructionists, psychiatrists). (4) Character witnesses — persons testifying to the accused's good character. (5) Complainants — the alleged victims of the offence. (6) The accused themselves, if they choose to testify.
Compellability
Most witnesses can be compelled to attend court through a subpoena. Failure to comply with a subpoena can lead to a material witness warrant. Several categories of persons have limited or no compellability: the accused cannot be compelled by the Crown (section 11(c) Charter); spouses historically could not be compelled to testify against each other (the rule was modified by Bill C-32, in force since 2015, removing spousal incompetency in most cases); diplomatic and consular officials have certain immunities. Other privilege rules (solicitor-client, informer) restrict what witnesses can be required to testify about.
Witness protections
Several provisions protect witnesses, particularly vulnerable ones. Testimonial aids under section 486.1 (support person), section 486.2 (testimony behind a screen or via closed-circuit television), and section 486.3 (cross-examination through a court-appointed lawyer for self-represented accused) are available for child witnesses, witnesses with disabilities, and other vulnerable witnesses. Section 486.4 publication bans protect complainant identity in sexual offence cases. Witnesses can also receive informer privilege protection where they assisted police as confidential sources.
Witness reliability
Witness testimony is tested through cross-examination, comparison with other evidence, internal consistency, prior statements, and the witness's demeanour and credibility. Reliability and credibility are distinct: a witness can be credible (honest) but unreliable (mistaken). The trier of fact assesses both. Many criminal trials turn on careful credibility analysis applied to competing witness accounts.
Witnesses and the defence
Defence counsel routinely call witnesses — alibi witnesses, character witnesses, witnesses contradicting Crown evidence, expert witnesses. Decisions about which witnesses to call, and how, are central to trial strategy. Mass Tsang's criminal lawyers prepare witnesses carefully and treat witness selection as part of overall trial planning.
Related glossary terms
