Prosecutors and Expert Witnesses
| Author | Bibi Sangha/Kent Roach/Robert Moles |
| Pages | 27-54 |
CHAPTER
2
Prosecutors
and
Expert
Witnesses
This
chapter
sets
out
some
of
the
important
elements
about
how
things
ought
to
be
done
—
the
rhetoric
—
in
the
conduct
of
legal
proceedings.
The
focus
is
on
the
role
of
prosecutors
and
expert
witnesses,
both
of
which
play
a
critical
role
in
presenting
forensic
evidence
to
the
courts.
As
will
be
seen,
both
pros
ecutors
and
expert
witnesses
are
supposed
to
present
evidence
in
a
fair
and
impartial
manner
in
order
to
assist
the
court
in
making
reliable
and
careful
decisions
about
guilt
and
innocence.
In
this
chapter
we
explain
that
the
duty
of
a
prosecutor
is
not
just
to
obtain
a
conviction
but
to
act
fairly
in
presenting
relevant
evidence
to
a
court.
The
basic
principles
that
govern
the
conduct
of
prosecutors
are
common
to
each
of
our
three
main
jurisdictions.
However,
the
way
in
which
they
are
applied
in
practice
can
be
quite
different,
as
we
see
in
Part
Two
of
this
book.
We
also
explain
two
important
aspects
relating
to
the
conduct
of
expert
witnesses.
The
first
is
what
the
law
requires
of
them
in
order
to
be
regarded
as
an
expert
and
to
grant
them
special
privileges
in
terms
of
what
they
can
say
to
the
court
in
the
conduct
of
legal
proceedings.
The
second
is
to
set
out
some
of
the
ethical
principles
that
are
laid
down
in
codes
of
conduct
and
meant
to
guide
their
conduct
before,
during,
and
after
they
give
evidence
in
court.
Expert
witnesses
are
an
exception
to
the
general
rule
that
witnesses
are
not
allowed
to
express
their
opinions
about
what
the
evidence
in
legal
proceedings
means.
Experts,
the
law
tells
us,
are
people
who
are
appropriately
qualified
and
with
proper
experience.
In
certain
circumstances,
they
are
allowed
to
assist
the
jury
by
advising
what
inferences
might
be
drawn
from
the
available
evidence.
However,
it
is
always
up
to
the
jury
to
determine
if
they
accept
the
advice.
27
18
Forensic
Investigations
and
Miscarriages
of
Justice
The
UK
Law
Commission
summed
up
the
position
in
its
2009
Discussion
Paper
setting
out
the
law
relating
to
the
role
of
expert
witness.
It
referred
to
the
1984
South
Australian
case
of
R.
v.
Bonython'
as
correctly
expressing
the
ap
plicable
principles.
We
explain
in
this
chapter
that
the
more
recent
Australian
case
of
Makita
v.
Sprowlef
endorses
key
aspects
of
the
Bonython
position,
and
does
so
by
linking
the
discussion
to
important
British
cases.
The
net
effect,
it
may
be
said,
is
that
the
Australian
and
British
positions
are
closely
aligned
on
these
issues
as
is
the
Canadian
position.
In
substance,
the
cases
say
that
an
expert
opinion
must
be
based
upon
clearly
stated
facts
that
have
been
(or
will
be)
established
by
properly
admis
sible
evidence
in
the
case
(the
relevance
issue).
Scientific
principles
and
the
reasoning
that
relates
them
to
the
facts
of
the
case
must
also
be
correct
and
clearly
articulated
by
the
expert
(the
reliability
issue).
It
is
clear
that
an
expert
witness
must
not
engage
in
speculation
or
testify
in
areas
that
lie
outside
of
his
or
her
expertise.
There
are
many
codes
of
conduct
to
assist
experts
in
properly
understand
ing
their
role
in
legal
proceedings,
and
we
give
details
of
some
of
these.
The
codes
are,
in
effect,
simplified
expressions
of
the
underlying
legal
principles.
They
are
usually
propounded
by
the
relevant
associations
as
an
educational
tool
to
reinforce
and
remind
their
members
of
key
aspects
of
their
professional
duties.
The
codes
say
that
expert
witnesses
are
expected
to
act
in
a
fair
and
balanced
manner;
they
are
not
supposed
to
act
in
the
interests
of
either
the
prosecution
or
the
defence.
They
are
there
to
assist
the
court
to
understand
the
evidence
and
the
issues
involved.
Important
problems
are
associated
with
the
introduction
of
experts
into
any
legal
proceedings.
Jurors
(and
judges)
may
be
tempted
to
accord
undue
deference
to
them.
The
defence
may
be
unable
to
afford
or
to
find
others
of
similar
standing
to
challenge
those
put
forward
by
the
prosecution.
It
will
be
clear
from
the
cases
we
look
at
in
Part
Two
that
there
have
been
many
cases
where
inappropriate
expert
evidence
has
been
admitted.
That
will
give
rise
to
some
consideration
as
to
how
such
evidence
was
admitted.
Was
it
because
the
judges
were
not
sufficiently
skilled
in
evaluating
the
scientific
issues
involved
or
had
not
sufficiently
appreciated
what
the
rules
set
out
in
this
chapter
required
of
them?
Had
the
judges
perhaps
been
too
indecisive
in
keep
ing
questionable
evidence
from
the
jury?
1
R.
v.
Bonython
(1984),
38
S.A.S.R.
45
at
paras.
46-47;
UK
Law
Commission,
The
Admis
sibility
of
Expert
Evidence
in
Criminal
Proceedings
in
England
and
Wales,
Consultation
Paper
190
(Norwich:
The
Stationery
Office,
2009)
[Law
Commission,
“
Admissibility
”
].
2
Makita
(Australia)
Pty.
Ltd.
v.
Sprowles,
[2001]
NSWCA
305
[Makitdf
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