Type of document: Prosecution Directive
Effective date: November 14, 2017

Expert evidence is admissible where the subject matter requires specialized knowledge that is likely outside of an ordinary person’s knowledge or experience and is necessary in order for the court to reach a correct judgment about the issue.

When considering the use of expert evidence, Prosecutors should be guided by the general duty to see that justice is done in the circumstances of the particular case. The Prosecutor who tenders expert evidence must ensure that it is presented to the court with no more, and no less, than its legitimate force and effect.

The role of an expert in the criminal justice system is a neutral one that requires independence and objectivity at all stages of her involvement.

Retaining an expert

Prosecutors should decide at the earliest possible opportunity whether expert evidence is required. This should be done early in the proceeding to minimize the delay occasioned by retaining an expert and in order to meet the notice and disclosure requirements set out in the Criminal Code.

The Prosecutor must obtain prior approval from the Director or designate before retaining and paying an expert for the purpose of giving evidence or assisting the Prosecutor in preparing for trial.


The Prosecutor must generally disclose all relevant information in her possession relating to the charges against an accused. This includes all expert reports, summaries of expert opinions and, if requested, any underlying material relied upon by the expert where it is practicable to do so.

The Prosecutor is not obliged to disclose information that is irrelevant, protected by privilege or that is recognized at common law or by statute as an exception to the duty to disclose.

The Prosecutor’s duty to disclose is ongoing throughout the trial and appeal process and continues after those processes have concluded.

Reference should also be made to the Disclosure Directive.

Presenting expert evidence

In preparing experts for their testimony, Prosecutors should ascertain from the expert the limitations on the expert opinion including their qualifications and any limitations on the inferences that can be reliably drawn from the expert evidence. When presenting the expert evidence in court, Prosecutors should make every effort to ensure that those limitations are fully impressed upon the court.

Where an expert expresses to the Prosecutor a concern that their evidence has left a misleading or inaccurate impression with the Court, the Prosecutor must immediately disclose this to the defence and in circumstances where the concerns are justified, it must be conveyed to the Court.

Reporting concerns

A Prosecutor must report to her Crown Attorney adverse judicial findings or comments about an expert or her own concerns about an expert’s participation in the criminal justice system.

The Crown Attorney must forward any adverse judicial findings or comments about an expert or any concerns expressed by a Prosecutor regarding an expert’s participation, to the Director, who will forward it onto the Assistant Deputy Attorney General - Criminal Law Division.