Using Expert Witnesses in Criminal Defence

In many criminal cases, the evidence goes beyond what ordinary witnesses can explain. That’s where expert witnesses play an important role. An expert witness is a professional with specialized knowledge—such as in medicine, forensics, psychology, or toxicology—who can help the court understand complex issues. Their testimony can strengthen your defence by offering impartial, credible opinions that challenge the prosecution’s case. At Davidson Gregory, we carefully assess when to use expert witnesses and how their evidence can best support your defence strategy.

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Using Experts to Defend Your Criminal Charge

In a criminal trial, the Crown prosecution and your lawyer may call witnesses to provide evidence. Most witnesses are ordinary individuals, but an “expert witness” is someone with sharp knowledge on a particular topic who can assist the court in understanding a specific issue. An expert witness delivers a professional opinion, while all other witnesses are confined to relaying facts within their sphere of knowledge, observation and experience.

Determining Expert Witnesses

The trial judge will determine if an individual is qualified as an expert and, if so, what the nature and scope of the proposed evidence will be. The judge will not permit the expert to provide an opinion on common matters in which he or she has no special skills, knowledge or training. Further, the evidence is expected to be impartial; there must not be any bias or appearance of bias.

Proving Expert Evidence

In order to prove expert evidence, the law requires that the following issues be given consideration:

Selecting the precise question with respect to which the opinion is sought;
Ensuring the person is qualified to answer that precise question;
Determining the assumptions necessary to arrive at an opinion and ensuring these assumptions can be proven; and
Ensuring the expert opinion meets the admissibility requirements.

Admissibility of Expert Evidence

The admissibility of expert evidence depends on four “rules-based” criteria, set out in the case of R. v. Mohan, 1994:

The evidence provided must be both logically and legally relevant;
The evidence must be necessary to assist in drawing the correct inference;
The person giving the evidence must have the required qualifications of an expert;
There must be the absence of any other exclusionary rule; and
The admissibility of expert evidence also depends on the court’s cost/benefit analysis in its role as gatekeeper.

Calling a Witness to a Criminal Trial

Expert witnesses and other witnesses can be called upon by subpoena to testify. They may be required to appear in court to testify or produce documents related to the proceeding that are in his or her possession.

The defence is not obliged to call upon a witness but in the event that they do, the prosecutor has the right to cross-examine him or her. Each witness must answer all questions under oath, unless the Judge declares otherwise.

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Criminal Defence Areas of Practice

Drug Charges Defence

Drug charges are serious, but a well-prepared defence can protect your future. We challenge improper searches, test the evidence, and fight to ensure your rights are upheld at every stage of the case.

Weapons and Firearms Charges

Weapons charges can carry harsh penalties. We provide skilled defence, challenging the legality of searches, possession claims, and the procedures used to lay these serious criminal charges.

Sexual Offences and Misconduct

Sexual offence allegations require a strategic and sensitive approach. We provide thorough, discreet defence focused on protecting your reputation and ensuring fairness throughout the legal process.

Search and Seizure Defence

Illegally obtained evidence can be excluded with the right defence. We focus on your rights and challenge searches that violate legal standards or lack proper justification by law.

Domestic Violence Defence

Domestic violence charges can impact families and futures. We offer strong, compassionate defence, ensuring your story is heard, your rights are respected, and no detail is overlooked in court.

DUI and Impaired Driving Defence

DUI charges demand precise legal strategy. We examine traffic stop procedures, breath tests, and timelines to protect your license, freedom, and future from serious criminal consequences.

Commercial Crime

White-collar crime allegations often involve intricate legal and financial issues. We build clear, strategic defences that address complex documents, intent, and professional responsibilities.

Computer and Internet Crime

Cyber crime law evolves rapidly and requires technical expertise. We analyze digital evidence, challenge investigatory methods, and defend against internet-related allegations with precision.

Organized Crime

Organized crime charges come with heavy scrutiny and complex evidence. We fight hard to challenge surveillance, association claims, and any overreach in investigations or prosecution tactics.

Regulatory Discipline Defence

Facing professional discipline can be career-defining. We help defend licenses, reputations, and livelihoods with focused strategies that ensure due process and professional fairness throughout.

Bail Hearings

Timely bail is critical to your defence. We prepare compelling arguments for release, challenge detention, and work to secure reasonable conditions while your matter moves through the courts.

Physical Assault

Assault is considered a serious offence with heavy penalties, including a criminal record, or occasionally, a jail sentence. This can affect you, your family, and your financial future.

Murder

Murder is the most serious criminal offence and if convicted, an accused is liable to a sentence of life imprisonment.