Every criminal case is ultimately decided based on evidence: the material a court is permitted to consider when deciding whether the Crown has proven a charge. Understanding, in general terms, what counts as evidence, how it is presented, and how witnesses are brought before the court is a useful foundation for understanding the rest of the criminal process. This guide provides a general overview of evidence and witnesses in an Ontario criminal case. It is general information only and not legal advice about a specific case; the detailed mechanics of actually testifying and being cross-examined are covered in separate, more focused guides linked below.
Evidence rules can seem technical, but the underlying idea is straightforward: courts need reliable ways of establishing what actually happened, and rules of evidence exist to help ensure that what a judge or jury relies on is trustworthy and fair to consider, rather than simply whatever information happens to be available.
What Counts as Evidence?
In a criminal trial, evidence generally refers to the testimony, objects, documents, and other material that the court is permitted to consider in deciding the facts of the case. Not everything a person believes or has heard about a case automatically becomes evidence; it generally must be presented in a recognized form, such as through a witness's sworn testimony or an admissible document or exhibit, and must satisfy certain rules before a court can rely on it.
Evidence in a criminal case generally falls into a few broad categories, discussed below: testimonial evidence, physical or real evidence, documentary evidence, and expert evidence. Most cases involve some combination of these categories rather than relying on just one.
Testimonial Evidence
Testimonial evidence is evidence given by a witness, under oath or affirmation, describing what they personally observed, heard, or experienced. This can include testimony from a complainant, an eyewitness, a police officer describing their investigation, or other people with relevant firsthand knowledge. Testimonial evidence is central to most criminal trials, and its reliability is generally tested through direct examination and cross-examination. See our separate guides to testifying and cross-examination for the detailed mechanics of how this works in practice.
Physical or Real Evidence
Physical evidence, sometimes called real evidence, refers to actual objects connected to the alleged offence, such as a weapon, controlled substance, clothing, or other item recovered during an investigation. Physical evidence is often introduced through the testimony of the person who found, seized, or examined it, since a court generally needs to understand where an item came from and how it was handled before relying on it. How physical evidence was obtained can also matter a great deal; evidence gathered through an unlawful search, for example, may become the subject of a pretrial application. See our guide to pretrial applications and motions.
Documentary Evidence
Documentary evidence includes written or recorded material such as text messages, emails, business records, photographs, and video or audio recordings, including body-worn camera footage or 911 calls. Documentary evidence is generally introduced through a witness who can speak to its origin and authenticity, and, depending on its content, can raise its own admissibility questions, including whether portions of it amount to hearsay, discussed further below.
Expert Evidence
Expert evidence is testimony from a person qualified in a specialized field, such as forensic science, toxicology, or a particular area of medicine, who is permitted to offer an opinion on a technical matter beyond the general knowledge of a judge or jury. Before an expert can offer opinion evidence, a court generally must be satisfied that the person is properly qualified and that expert evidence on that topic is necessary and appropriate. Expert evidence can be significant in cases involving, for example, impairment, injury, or the analysis of digital or forensic material.
Relevance and Admissibility
Not all evidence that exists is automatically usable at trial. Two basic concepts govern whether a court will consider a piece of evidence: relevance and admissibility. Relevance asks whether the evidence has some logical connection to a fact that actually matters in the case. Admissibility asks whether, even if relevant, the evidence is allowed to be used, given the various rules of evidence that can exclude certain material, such as hearsay, evidence obtained in breach of the Charter, or evidence whose potential to unfairly prejudice the accused outweighs its value.
A judge generally decides admissibility questions, often through a voir dire held separately from the main evidence, particularly for more contested issues. See our guide to pretrial applications and motions for more on how these issues are argued and decided.
Hearsay: A Plain-Language Overview
One of the most commonly discussed evidence rules is the rule against hearsay. In plain language, hearsay is generally an out-of-court statement, made by someone other than the witness currently testifying, that is being offered to prove the truth of what it says. For example, if a witness testifies, "My neighbour told me she saw the defendant leave the scene," and that testimony is being used to prove the defendant actually left the scene, it is generally hearsay, because the neighbour, not the testifying witness, is the person with firsthand knowledge, and the neighbour is not present to be cross-examined about what they actually saw.
Hearsay is generally inadmissible, because the person who actually made the original statement is not before the court and cannot be cross-examined about its accuracy, which raises concerns about reliability. That said, the hearsay rule has a number of well-established exceptions, developed over time through case law, that allow certain out-of-court statements to be admitted in specific circumstances where there are other, sufficient guarantees of reliability. Whether a specific statement falls under an exception is a legally technical question that depends heavily on the exact circumstances, and is best assessed by a lawyer reviewing the actual evidence in a case.
Hearsay is one of the more misunderstood evidence concepts. Not everything that sounds like secondhand information is automatically excluded, and not everything a witness saw or heard directly is automatically admissible. A lawyer reviewing the disclosure can identify genuine hearsay issues in a specific case.
The Burden and Standard of Proof
Evidence in a criminal case is ultimately assessed against the requirement that the Crown must prove every element of the offence beyond a reasonable doubt. This is a demanding standard, and it places the burden squarely on the Crown; an accused person does not generally have to prove innocence or disprove the Crown's evidence. See our separate guide to the burden of proof for a fuller explanation of how this standard works in practice.
How Witnesses Are Compelled to Attend
Witnesses do not always attend court voluntarily, and the criminal process has a formal tool to require attendance: a subpoena, sometimes called a summons to a witness. A subpoena is a court document that legally compels a named person to attend court on a specified date to give evidence, and, where relevant, to bring specified documents or items with them. A witness who is properly served with a subpoena and fails to attend without a valid excuse can face legal consequences, including a warrant for their arrest to compel attendance.
Either the Crown or the defence can arrange for a subpoena to be issued for a witness whose testimony is relevant to the case. This tool exists because the fair resolution of a criminal case often depends on the court hearing from people who might not otherwise choose to come forward or participate voluntarily.
Being a Witness
Being a witness, whether as a complainant, a bystander, or someone who provided assistance to police, can be a significant experience, and Ontario has resources specifically for people going through this. See our guide for victims and witnesses for general information about support available to people participating in the criminal process in this role. The specific mechanics of what happens once a witness is called to testify, including direct examination and cross-examination, are addressed in our dedicated guides to testifying and cross-examination, rather than repeated in full here.
Frequently Asked Questions
What is the difference between relevance and admissibility?
Relevance asks whether evidence logically relates to a fact that matters in the case. Admissibility asks whether, even if relevant, the evidence is legally allowed to be used, given rules such as those governing hearsay or Charter breaches.
Is hearsay ever allowed in court?
Yes, in certain circumstances. While hearsay is generally inadmissible, there are recognized exceptions that can allow specific out-of-court statements to be admitted where there are sufficient guarantees of reliability.
What is a subpoena?
A subpoena is a court document requiring a named person to attend court on a specific date to give evidence, and, where relevant, to bring specified documents or items.
What happens if a witness ignores a subpoena?
A witness who is properly served and fails to attend without a valid excuse can face legal consequences, including a warrant to compel their attendance.
Is expert evidence automatically accepted by the court?
No. A court must first be satisfied that the person is properly qualified and that expert opinion evidence is necessary and appropriate on the specific issue before it can be relied on.
Where can I learn about actually testifying or being cross-examined?
This overview focuses on the general categories and rules of evidence. For the practical mechanics of giving testimony and being cross-examined, see our dedicated guides to testifying and cross-examination.