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An explanation of opinion evidence versus lay witness evidence in the case of R v TL.

R v TL is an ongoing case before the Provincial Court of Alberta. It has been a legally complex and long-drawn out case. My client is alleged to have committed an aggravated assault upon his 4-year old daughter. The Crown theory is that the young girl’s stepfather assaulted her. The Defence theory is that the girl slipped and fell in the bathtub. There was no direct evidence of what actually happened. The prosecution’s case is premised largely on the opinion of two medical experts who concluded that the injuries suffered were indicative of abuse.

Expert witness testimony requires specific legal considerations that require scrutiny. This is because, if a witness is declared an expert by the Court, then the expert can give opinion evidence. Opinion evidence refers to evidence of what the witness thinks or believes or infers with respect to the facts and that is distinguished from personal knowledge which is what the Court will normally assess. Traditionally, the trier of fact assesses viva voce evidence from non-expert witnesses. The historical rule has been that a lay witness “may not give an opinion or draw an inference unless it … is helpful to the witness in giving a clear statement to the trier of fact in determining the issue”. The word “helpful” is the key and critical area here. In 1898, Thayer wrote:

"There is ground for saying that, in the main, any rule excluding opinion evidence is limited to cases where, in the judgment of the court, it will not be helpful to the jury. (Thayer, A Preliminary Treatise On Evidence (South Hackensack: Rothman Reprints, 1965) at 525.)"

This ongoing case demonstrates the distinct types of evidence a court may hear. Lay witnesses testify to what they saw and experiences. Expert witnesses may give evidence on what his or her opinion is on the fact pattern at issue. It is important for your lawyer to understand the distinct types of evidence and how it can be used. Sometimes, as your defence lawyer, we may suggest and give you legal advice that we need to retain an expert on your behalf to raise doubt.

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