Qualifying Police Officers to Give Expert Opinion in Drug Cases

Opinion evidence is presumptively inadmissible. The test for the admissibility of opinion or “expert” evidence begins with consideration of the four Mohan criteria:
•                  relevance
•                  necessity
•                  the evidence is not contrary to an exclusionary rule
•                  a properly qualified expert. 
 See: R v Mohan 1994 CanLII 80 (SCC), [1994] SCJ No 36.
Properly Qualified Expert
The party seeking to have the witness qualified must prove that the witness has acquired special or peculiar knowledge through study or experience in respect of the matters on which he or she undertakes to testify.
 Mohan, at para 27. 
Proof that a proposed expert witness is properly qualified includes the requirement that the expert be independent, objective and impartial.
White Burgess 2015 SCC 23 (CanLII) at para 48, Mouvement laïque québécois v. Saguenay 2015 SCC 16 (CanLII) para.106.

Qualifying Police Officers in Drug Cases
Police officers are sometimes used by the Crown at trial to give expert opinion evidence with regard to, among other things, the methodology of drug trafficking, and the subculture of drug use, including pricing; distribution and street use of particular drugs.
Police officers have been qualified to give opinion evidence with respect to pricing, packaging and usage.
R v Pham 2013 ONSC 4903 (CanLII) at para 29.
The fact that the officer’s experience includes anecdotal sources including reports from drug users does not preclude the admissibility of that evidence.
 R v Dominic 2016 ABCA 114 (CanLII) at para 22-23.
The fact that the officer is not involved in the particular investigation and otherwise understands the role of an expert witness and the limits on that role may be sufficient to answer concerns about objectivity.
R. v. Nguyen, 2017 ONCJ 93, at para. 8.

Probative value v. Prejudicial Effect
If the Crown proves the proposed evidence meets the Mohan criteria, the court must then consider whether the probative value of the evidence exceeds any prejudicial effect – is the evidence worth what it costs?
 White Burgess at para 2; R v Abbey 2009 ONCA 624 (CanLII).
Note that on this admissibility voir dire the court decides only whether the evidence is worthy of being heard, not the ultimate question as to whether the evidence will be accepted or given weight.
Abbey, at para.89.


See R. v. Nguyen, 2017 ONCJ 93


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