4.12.2 - Opinion Evidence: DNA Evidence1
4.12.2.1 - DNA Evidence: Bench Notes
Impact of the Uniform Evidence Act
Part 3.3 of the UEA substantially changes the law as it relates to opinion
evidence.2
Those changes have no direct impact on the subject matter of these
bench notes
What is DNA Evidence?
1.
“DNA evidence” refers to a type of expert evidence in which the DNA
of a sample found at a crime scene (a “forensic sample”) is compared
with a DNA sample provided by the accused (a “reference sample”).
2.
As DNA evidence is a type of expert evidence, the principles outlined
in Bench Notes: General Principles of Expert Evidence apply (subject
to any modifications noted below).
3.
DNA evidence examines and compares the DNA contained in
chromosomes. DNA is consistent throughout a human body (R v Noll
[1999] 3 VR 704; R v Jarrett (1994) 62 SASR 443).
4.
There are two ways in which DNA can be examined and compared:

“Nuclear DNA testing” examines and compares the DNA
contained in the nucleus of a cell. Nuclear DNA is unique to an
individual (apart from identical twins).

“Mitochondrial DNA testing” examines and compares the DNA
contained in the mitochondria. This does not produce a unique
result, as mitochondrial DNA is inherited entirely from the
mother, and so is the same between siblings (R v Rye [2007]
VSCA 247).
What does a DNA “Match” Establish?
5.
The DNA strands in chromosomes are held together by base pairs.
There are approximately three billion base pairs, and about three
million of those vary between individuals (R v Noll [1999] 3 VR 704;
1
This document was last updated on 29 June 2015.
2
See further Bench Notes: General Principles of Opinion Evidence.
R v Jarrett (1994) 62 SASR 443).
6.
Due to the uniqueness of nuclear DNA, if all base pairs of two nuclear
DNA samples were tested and matched, it would be possible to say
that the samples came from the same person (or an identical twin).
7.
However, DNA testing does not measure and compare every single
base pair of the relevant samples. It only measures and compares
the length of certain strings of base pairs at known positions called
“loci” (R v GK (2001) 53 NSWLR 317; R v Pantoja (1998) 88 A Crim
R 554).
8.
This means that, even where there is a “match” between two
samples, it is not possible to say with certainty that they came from
the same person. One of the samples could have come from a
different person who happens to have the same string length of base
pairs at the loci that were tested (R v GK (2001) 53 NSWLR 317; R v
Pantoja (1998) 88 A Crim R 554).
9.
Thus, a “match” between the accused’s DNA and a sample taken
from the crime scene only establishes that the accused could be
responsible for the forensic sample. That is, the evidence does not
exclude the accused from responsibility (R v GK (2001) 53 NSWLR
317; R v Pantoja (1998) 88 A Crim R 554).
10. For DNA evidence to have any further probative force, evidence must
also be given by a suitably qualified expert about the probability of a
match with a random member of the population (R v Noll [1999] 3
VR 704; R v Rye [2007] VSCA 247).
11. Expert witnesses may state their conclusions about the probability of
a match with a random member of the population in the following,
equally mathematically correct, forms:

As a ratio of the number of people in Australia who would be
expected to have the same DNA profile (e.g. 1 in 100);

As a ratio of the number of people in Australia who would not
be expected to have the same DNA profile (e.g. 99 in 100);

As a percentage of the number of people in Australia who would
be expected to have the same DNA profile (e.g. 1%);

As a percentage of the number of people in Australia who would
not be expected to have the same DNA profile (e.g. 99%);

As the number of people in Australia who would be expected to
have the same DNA profile (e.g. 225,096 people);3 and
There are currently estimated to be 5,547,500 people in Victoria and
22,509,625 people in Australia. Therefore, if the probability of a match with a
3

As the number of people in Australia who would not be expected
to have the same DNA profile (e.g. 22,284,528) (see Aytugrul v
R [2010] NSWCCA 272 per McClelland CJ at CL).
12. As all of these values express the same information there is no
reason to prefer one method of expression over another (provided
the numbers are accurately calculated). Experts should express their
conclusions in a way that the jury can readily comprehend (Aytugrul
v R [2010] NSWCCA 272 per Simpson and Fullerton JJ (McClelland CJ
at CL contra). See also R v GK (2001) 53 NSWLR 317; R v Doheny &
Adams [1997] 1 Cr App R 369).
13. To avoid the risk that the jury may be overwhelmed by exceptionally
high probabilities or likelihood ratios, witnesses may be permitted to
present the statistical evidence concerning the probability of a match
qualitatively rather than quantitatively, by describing the probability
of a match with the accused as “strong”, “very strong” or “extremely
strong” (see Forbes v R (2009) 167 ACTR 1).
14. To reach these conclusions, experts rely on the frequency with which
certain DNA string lengths occur in the general population (R v GK
(2001) 53 NSWLR 317; R v Berry & Wenitong (2007) 17 VR 153).
15. These frequencies are recorded in databases, which have been built
up using previous genetic testing. A database (and the consequent
results obtained from that database) will only be reliable if it contains
a representative sample of the general community or, if the offender
is from a specific ethnic group, the relevant ethnic community (R v
Noll [1999] 3 VR 704; R v Pantoja (1996) 88 A Crim R 554).
Samples from More than One Person
16. Where a forensic sample contains DNA material from several people,
an expert witness may give evidence on the probability of it
matching a specified group of people (rather than having come from
a group of randomly selected people) (R v GK (2001) 53 NSWLR
317; R v Berry & Wenitong (2007) 17 VR 153).4
17. The expert may also give evidence on the likelihood of the DNA
having come from one specified set of contributors (e.g., those
alleged by the prosecution) rather than another (e.g., those alleged
by the defence). This will allow the jury to assess the relative
random member of the population is 100:1, then there are approximately 55,475
people in Victoria that would match that sample at any given time, or 225,096 in
the whole of Australia.
The expert uses population statistics to determine the probability of each string
length that is measured. Provided each string length is independent, these
probabilities are multiplied together to determine the probability of all string
lengths being detected in a random sample.
4
probability of the prosecution and defence hypotheses (R v Berry &
Wenitong (2007) 17 VR 153).
What does a Failure of DNA Samples to “Match” Establish?
18. If accepted, evidence that the accused’s DNA sample does not match
a sample taken from the crime scene establishes that the accused is
not responsible for the forensic sample (R v GK (2001) 53 NSWLR
317; R v Pantoja (1998) 88 A Crim R 554).
Standard of Proof
19. As DNA evidence is circumstantial evidence, the prosecution only
needs to prove that the accused is responsible for a forensic sample
beyond reasonable doubt if that evidence is indispensable to the
prosecution case (R v Juric [2003] VSC 382; R v Berry & Wenitong
(2007) 17 VR 153; R v Kotzmann [1999] 2 VR 123; Shepherd v R
(1990) 170 CLR 573; R v Noll [1999] 3 VR 704).
20. This will usually only be the case if there is no other evidence linking
the accused to the offence, or if the other evidence is especially weak
(R v Juric [2003] VSC 382; R v Berry & Wenitong (2007) 17 VR 153;
R v Kotzmann [1999] 2 VR 123; Shepherd v R (1990) 170 CLR 573;
R v Noll [1999] 3 VR 704; Forbes v R (2009) 167 ACTR 1).
Jury Directions
21. DNA evidence is not a class of evidence that calls for special
directions in every case (R v Berry & Wenitong (2007) 17 VR 153; R
v Karger (2002) 83 SASR 135).
22. Where DNA evidence is given, the judge must:

Ensure that the jury understands the issues and the evidence in
the case; and

Give any directions that are necessary to ensure that the jury
does not misuse the evidence.
23. Judges have traditionally accomplished these goals by giving a
careful summary and explaining the limitations of the evidence (R v
Berry & Wenitong (2007) 17 VR 153; R v Karger (2002) 83 SASR
135).
24. Following the Jury Directions Act 2015, a judge is not required to
summarise the evidence, but must identify so much of the evidence
the judge considers necessary to assist the jury to determine the
issues in the trial (Jury Directions Act 2015 ss65, 66).
25. The need for directions on DNA evidence will depend on whether any
directions are sought or whether there are substantial and
compelling reasons for giving a direction in the absence of any
request (Jury Directions Act 2015 ss14 - 16). See Bench Notes:
Directions Under Jury Directions Act 2015 for information on when
directions are required. See also Bench Notes: Judge’s Summing Up
on Issues and Evidence.
26. When directing the jury about DNA evidence, the following issues
may need to be addressed if they are in dispute:

The jury’s role in determining whether or not there is a match
between the forensic sample and the reference sample;

The jury’s role in assessing the accuracy and reliability of the
expert evidence; and

The consequences of finding there was (or was not) a match.
27. The judge may also need to address any fallacies put forward by the
parties.
Is there a Match?
28. The judge should tell the jury that it is a question of fact for them
whether there is a match between the forensic sample and the
reference sample (R v Pantoja (1998) 88 A Crim R 554; R v Karger
(2002) 83 SASR 135).
29. This will usually be determined by the jury using the evidence given
by the expert witnesses (R v Pantoja (1998) 88 A Crim R 554; R v
Karger (2002) 83 SASR 135).
30. Where there is evidence that suggests that the reference sample
does not match the forensic sample, and there is a reasonable
possibility that that evidence is correct, the jury must find that the
accused was not responsible for the forensic sample (R v Pantoja
(1996) 88 A Crim R 554).
31. In such circumstances, the jury should be directed to find that the
accused was not responsible for the forensic sample, even if other
tests have indicated that the reference sample and the forensic
sample matched. The jury may only rely on a match if the reference
sample matched the forensic sample at all loci that were tested (R v
Pantoja (1996) 88 A Crim R 554).
Was the Testing Accurate and Reliable?
32. The jury should consider whether the testing was accurate and
reliable (R v Pantoja (1998) 88 A Crim R 554; R v Karger (2002) 83
SASR 135).
33. In some cases, this may require the jury to consider whether the
evidence may have been affected by laboratory error (R v Karger
(2002) 83 SASR 135).
34. The jury should also consider any limitations in the database used by
the experts to assess the probability of the sample coming from
someone other than the accused (R v Pantoja (1998) 88 A Crim R
554).
35. This may be particularly relevant where there is evidence that the
offender is a member of a particular ethnic group that may have
different genetic characteristics from the general community. The
jury should be directed to consider these limitations and their effect
on the statistical evidence (R v Pantoja (1998) 88 A Crim R 554).5
What Are the Consequences of the Jury’s Findings?
36. The judge should generally explain to the jury that evidence that the
accused’s DNA sample matches a sample taken from the crime scene
is not direct evidence that the accused committed the offence. It is
only circumstantial evidence, and must be considered in light of the
other evidence in the case (R v Karger (2002) 83 SASR 135; R v
Vivona Vic CCA 12/9/94).
37. Precisely what the jury should be told about the use they can make
of this circumstantial evidence will depend on the content of the
evidence:

Where there is evidence of a match, as well as evidence of the
probability of a match with a random member of the population,
the jury should be told that (if accepted) the evidence only
establishes that the accused could be the source of the forensic
sample, and indicates the likelihood that another person could
also be responsible for the forensic sample (R v Karger (2002)
83 SASR 135; R v Vivona Vic CCA 12/9/94).

Where there is only evidence of a match, the jury should be told
that (if accepted) the evidence cannot establish the accused’s
guilt, and can only demonstrate that the accused cannot be
excluded from the class of people who could be guilty (R v Rye
[2007] VSCA 247).

Where there is evidence that the samples do not match, the
jury should be told that (if accepted) the evidence establishes
that the accused is not responsible for the forensic sample (R v
GK (2001) 53 NSWLR 317; R v Pantoja (1998) 88 A Crim R
554).
Care must be taken when addressing this issue to ensure that the focus is on
the genetic characteristics of the offender’s ethnic group, rather than on the
genetic characteristics of the accused’s ethnic group. See R v Pantoja (1998) 88 A
Crim R 554.
5
Warning Against Misuse of Evidence
38. Expert evidence on the likelihood of a match with a random member
of the population is apt to mislead the jury. In particular, it creates a
risk that the jury will adopt the following erroneous reasoning
(known as the “prosecutor’s fallacy”):

Only one person in a million has a DNA profile that matches the
forensic sample;

The accused has a DNA profile that matches the forensic
sample;

Therefore there is a million to one probability that the accused
is responsible for the forensic sample and is guilty (R v Doheny
& Adams [1997] 1 Cr App R 369; R v Karger (2002) 83 SASR
135; R v GK (2001) 53 NSWLR 317).
39. This line of reasoning fails to recognise that even though only one
person in a million has a DNA profile that matches the forensic
sample, in a country the size of Australia (with over 21 million
people), it is statistically likely that the DNA of at least 20 other
people will also match that sample (R v GK (2001) 53 NSWLR 317; R
v Doheny & Adams [1997] 1 Cr App R 369).
40. It is not necessary to warn against the prosecutor’s fallacy in all
cases. The judge should consider the need for a direction based on
the following factors:

Whether a direction is requested;

The clarity of the witness’ evidence;

The purpose for which the evidence has been led;

The circumstantial nature of the evidence;

The risk of the jury misusing the evidence;

The arguments raised in the case (Jury Directions Act 2015 ss14
- 16; R v Karger (2002) 83 SASR 135).
41. If a direction is necessary, the judge should generally warn the jury
against engaging in the prosecutor’s fallacy when the DNA evidence
is led, and again in the final directions (R v Doheny & Adams [1997]
1 Cr App R 369; R v Karger (2002) 83 SASR 135; R v GK (2001) 53
NSWLR 317; Latcha v R (1998) 127 NTR 1).
42. The judge may also warn the jury not to disregard the strength of
the probability of a match. While DNA evidence is not capable of
proving to a scientific certainty that the accused is guilty, it may be
strong circumstantial evidence of guilt (R v GK (2001) 53 NSWLR
317).
43. Where the probability of a match is sufficiently high, the jury should
consider the fact that there is no evidence connecting any other
(random) people with a matching DNA profile to the offence (R v GK
(2001) 53 NSWLR 317; R v Doheny & Adams [1997] 1 Cr App R
369).