Scientific evidence and the criminal law: lessons from brain-based lie detection

AuthorJohn Danaher
PositionB.C.L. (U.C.C.), LL.M. (Dub.), Ph.D. Candidate and I.R.C.H.S.S. Scholar, University College Cork
2010] Scientific Evidence and the Criminal Law 1
Science is a powerful tool with many potential forensic
applications. Archimedes provides an illustrative example.1
Archimedes was the most famous scientist of his age, notable for
his practical applications of theoretical knowledge. Hiero, the
king of Syracuse, enlisted Archimedes’s help in resolving his own
quasi-legal dilemma. He believed he had been duped by the
goldsmith who had made his crown. Hiero had asked for the
crown to be made of pure gold, but suspected that silver and
copper had been added in order to increase the goldsmith’s profit
Archimedes knew that silver and copper were lighter than
gold, and would take up more space (i.e. have a greater volume)
than an equal weight of gold. So in order to determine whether
copper and silver had been added, Archimedes simply needed to
work out the volume of the crown. This was easier said than
done, since the most obvious way to work out the volume would
be to melt the crown. This was not an option. How could the
matter be resolved?
* B.C.L. (U.C.C.), LL.M. (Dub.), Ph.D. Candidate and I.R.C.H.S.S. Scholar,
University College Cork. The author would like to thank the Irish Research
Council for the Humanities and Social Sciences for their support of his
research. Comments and inquiries can be directed to: johndanaher1984
1 There seems no doubting that Archimedes discovered the principles of
hydrostatics. Whether this particular story about Hiero and the goldsmith is
true is a separate question. One is always slightly sceptical of historical
anecdotes of this sort. I originally encountered the story in Asimov, I.,
Breakthroughs in Science (Scholastic Magazines, 1959). However, there is
reason to doubt the story in its traditional form. The best discussion I have
found is on the Archimedes webpage run by Chris Rorres. He points out that a
different technique may have been used than that suggested above.
Judicial Studies Institute Journal [2010:1
Legend has it that a bath provided the solution. As he
lowered himself into the water, he noticed how some liquid
spilled-out over the edge, a phenomenon known as displacement.
He realised that the volume of water that was displaced was equal
to the volume of his body. This was a general principle that could
be put to use in ascertaining whether the crown was made of pure
gold or not. Using the principle he had discovered, he determined
that copper and silver had indeed been added to the gold in the
crown. Hiero executed the goldsmith.
We see here how a general scientific law or principle can
be put to use in determining someone’s legal fate. But questions
abound: What if Archimedes got the principle wrong? Would it
not then be terrible that a man had died because of mistaken
fealty to Archimedes’s insight? Is it not incumbent on us to
ensure that the scientific evidence used in making legal decisions
meets certain epistemic standards? How can we ensure that this is
done? These questions lie at the heart of this article.
The article is written against the backdrop of proposed
changes to the law in both Ireland and England with respect to the
admissibility of scientific evidence.2 Law reform bodies in both
jurisdictions are currently seeking to enhance the gatekeeping role
played by the judge when it comes to such admission. This would
require a greater critical engagement with the nuances,
complications and limitations of scientific inquiry.3
The enhancement of the judicial gatekeeping function is
something of which I am broadly supportive. But it has to be
approached with the right attitude and the right tools. This article
aims to provide both. In terms of attitude, it argues that critical
engagement with the nature of scientific inquiry is essential, not
just in aiding the fact-finding mission of the court, but in
2 See UK Law Commission, The Admissibility of Expert Evidence in Criminal
Proceedings in England and Wales (Law Com, CP No. 190, April 2009)
hereinafter “Admissibility of Expert Evidence”, available at
uk/docs/cp190.pdf. For the Irish equivalent, see Expert Evidence (LRC CP 52,
December 2008), hereinafter “Expert Evidence”. At the time of writing, final
reports were pending.
3 I will provide a brief outline of the proposed tests later in this article,
the relevant sections of the consultation papers are as follows: Admissibility of
Expert Evidence (previous note), part 6; and Expert Evidence (previous note),
chapter 2, section G.
2010] Scientific Evidence and the Criminal Law 3
maintaining the integrity of a liberal democratic system. In terms
of tools, it aims to illustrate the basic theoretical and
methodological grounding that is needed for critical engagement.
It does so by eschewing an abstract and general discussion
of the relevant issues. There will be no comparing and contrasting
of the different proposed tests of evidential reliability, nor will
there be a general review of the problems courts have had with
scientific evidence. These topics have been covered at length
Instead, this article provides an extended analysis of just
one type of scientific evidence, namely brain-based lie detection
in criminal trials. This practical example will illustrate clearly and
forcefully the tools that are required for a critical engagement
with scientific evidence and highlight the need for that critical
Before proceeding with an outline, it is worth pausing to
answer the question: why brain-based lie detection? In recent
years, increasing attention has been paid to the potential legal
applications of the neurosciences.5 Enhanced tools for
investigating, imaging and manipulating the brain have
encouraged much academic speculation about neuroethics,
neurolaw, neuromarketing and other fanciful neuro-ticisms.6
But it is not all just idle speculation: there have been several
attempts, of varying success, to offer neuroscientific technologies
4 See Expert Evidence (note 2 above), chapter 2 for an overview of this topic.
5 The most conspicuous example of which is probably the MacArthur-funded
Law and Neurosciences Project. See Academic
articles on the topic are abundant. A representative sampling can be found in
Zeki, S. and Goodenough, O., Law and the Brain (Oxford: OUP, 2006).
Recent conferences in the area include “The Law and Neuroscience
Colloquium” University College London, July 6-7 2009; and “Law and
Neuroscience: Our Growing Understanding of the Human Brain and Its Impact
on our Legal System”, organised by the European Science Foundation and held
at Hotel Villa del Mare, Acquafredda di Maratea, Italy from 26-30 October
6 Examples abound, the setting up of the Neuroethics Society (of which the
present author is a member) (see being conspicuous
among them. A neuroethics journal is now published by Springer and the
American Journal of Bioethics dedicates three issues per year to neuroethics
alone. See Illes, J., Neuroethics: Defining the Issues in Theory, Practice and
Policy (Oxford: OUP, 2006), for an overview of this academic movement.

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