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

• Author: John Danaher
• Position: B.C.L. (U.C.C.), LL.M. (Dub.), Ph.D. Candidate and I.R.C.H.S.S. Scholar, University College Cork
• Pages: 1-37

2010] Scientific Evidence and the Criminal Law 1

SCIENTIFIC EVIDENCE AND

THE CRIMINAL LAW: LESSONS FROM

BRAIN-BASED LIE DETECTION

JOHN DANAHER*

I. SCIENTIFIC EVIDENCE AND THE JUDICIAL GATEKEEPER

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

margin.

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

@gmail.com

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.

See http://www.math.nyu.edu/~crorres/Archimedes/contents.html.

Judicial Studies Institute Journal [2010:1

2

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 www.lawcom.gov.

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

elsewhere.4

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

engagement.

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 http://www.lawneuro.org. 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

2009.

6 Examples abound, the setting up of the Neuroethics Society (of which the

present author is a member) (see www.neuroethics.com) 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.