Using Experts to Defend Your Criminal Charge
If you have a criminal trial, the Crown prosecution and your lawyer may call witnesses to give evidence about what they know. Most witnesses are ordinary individuals; they may have seen or heard an incident or accident occur or heard others talking about it. By contrast, an “expert witness” is a witness with knowledge about a particular topic that can assist the court in understanding an issue being argued in the trial. An expert witness can give a professional opinion, while all other witnesses can only relay facts within his or her 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 expert evidence” will be. The proposed expert must be able to provide personal opinions based on some scientific knowledge and not just based on their experience, knowledge from “some” literature and interviews. The judge will not permit the expert to provide an opinion on common matters or 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.
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 CanLII 80 (SCC), [1994} 2 S.C.R. 9:
- The evidence provided must be relevant (both logically and legally);
- 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 and;
- There must be the absence of any other exclusionary rule.
- The admissibility of expert evidence also depends on the court’s cost/benefit analysis in its role as gatekeeper as a result of the case of R. v. Sekhon, 2014 SCC 15.
There are situations where qualified expert evidence may be excluded. For example, if the evidence has the potential to distort the fact-finding process or if time and cost required outweigh its probative value, the evidence may be excluded. These exclusions came about from the case of R. v. D.D.  2 SCR 275.
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 in sought;
- Ensuring that the experience is qualified to answer that precise question;
- Determining the assumptions necessary to arrive at an opinion and ensuring that these assumptions can be proven; and
- Ensuring that the expert opinion meets the admissibility requirements.
Types of Expert Witnesses
When Mr. Gregory determines that the use of an expert is necessary to defend the case, he may draw from experts across North America to give their testimony. Mr. Gregory has used experts for several types of criminal charges, including for fraud, narcotics, impaired driving, sexual assault, or firearms offence charges in Edmonton. The type of experts Mr. Gregory may use in a criminal case include:
- Medical experts, such as the top psychiatrists, psychologists, physicians and pharmacologists;
- Chartered Accountants & tax experts, particularly in commercial crime and tax evasion cases;
- Polygraph experts;
- Private investigators;
- Handwriting and document analysis experts;
- Alcohol experts;
- Accident reconstruction experts;
- Dog sniffing experts in narcotics cases;
- Other experts.
Calling a Witness to a Criminal Trial
Expert witness and other witnesses can be called upon by subpoena to testify. They can be required to appear in court at a certain place and time in order to take the stand and give a testimony personally. Or, they may be required to produce documents related to a court proceeding that are in his or her possession.
Where a witness is called to a criminal case, the Crown will present its case and evidence first. The Crown may call a police officer or police investigator as an expert witness. The defence is not required to call any witnesses, but if this option is chosen, the prosecutor has the right to cross-examine any witnesses called. Each witness must answer all questions that are asked, unless the judge declares otherwise, under oath or affirmation. This means that the witness must swear or affirm to tell the truth, either on the basis of religion or a solemn belief.
Evaluating Conflicting Expert Evidence
In situations where the evidence of multiple experts conflict, a judge or jury must not choose one expert’s view over another and instead must give weight to each expert and review the opinions provided as a whole. However, like other witnesses, a trier of fact is free to accept some, none, or all of a witness’s evidence.
Using Rod J.A. Gregory for Your Legal Defence
Mr. Gregory has the legal experience to know which cases require the use of experts and which cases do not. He has extensive professional knowledge and is an excellent communicator and negotiator with the crown. Mr. Gregory has been a criminal defence lawyer for over 25 years, defending clients in Edmonton and western Canada.