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120 MANITOBA LAW JOURNAL |VOLUME 35 NUMBER 1
more skeptical view of forensic techniques mean as this new forensic science
makes its way into Canadian courts Might they, for example, have difficulty with
the new emphasis on statistics that this approach would require How will they
respond to controversies that might be engendered by this transition, such as
those that develop when standards of practice are in flux In this instance, we
have an advantage in that we can study a similar type of forensic evidence: DNA.
As we have seen, the NAS report demonstrates how different forensic DNA is
from other forms of forensic evidence. While it might be a model for other
forensic techniques, that does not mean that it was without its own difficulties
when it was introduced to Canadian courts. If other forensic techniques are to
follow the DNA model, might they expose cracks in Canadian law’s approach to
forensic science that will become evident when these other techniques begin to
adopt DNA methodology as their model If so, understanding the difficulties that
might be raised by the adoption of DNA as a model for forensic science will
require revisiting the difficulties that were encountered when DNA was first
introduced into Canadian courts.
IV.
QUESTIONING FORENSIC DNA TECHNOLOGY
When forensic DNA technology was first introduced, there were questions
about the interpretation of the sort of evidence given by DNA experts. 39 DNA
evidence depends on probabilistic statements of the likelihood of a false claim
that two DNA samples came from the same individual. 40 These probabilistic
statements require statistical, empirical verification and cannot be validated solely
based on individual clinical experience. The types of probabilistic claims made by
DNA evidence have raised a series of difficulties for courts concerned with the
potential for misuse of probabilistic claims. In the field of criminal forensics the
way DNA experts resorted to probabilistic statements in qualifying their claims
represented a significant change in the sort of evidence heard in the criminal
courtroom.
This section will characterize some of the debates that occurred in the context
of the early development of DNA technology, which are the debates that drove
the Canadian DNA cases.
Courtroom analysis of scientific expert evidence is constrained by the nature
of the technology used to produce and empirically validate the opinion evidence
presented by the putative experts in the particular specialty in question. For
example, a fingerprint examiner can identify an individual from an arrest record
39
40
See David H Kaye “The Admissibility of DNA Testing” (1991) 13 Cardozo Law Review 353 for a
brief, relatively early American discussion of the issues facing courts confronted with forensic
DNA.
NRC 1996, supra note 2 at 89-90.