Interrogations-and-Confessions-Handbook

294 A Psychology of Interrogations and Confessions
doubt, i.e. that there was no reasonable possibility that the confession could
have contributed to the conviction. 36
At trial, the defence will generally attack the reliability, rather than the voluntariness,
of the confession. Nevertheless, the Supreme Court has held that,
as part of the Sixth Amendment right to present a defence, a defendant cannot
be prohibited from offering evidence about ‘the physical and psychological environment
that yielded the confession’, because the jury will naturally want to
know why, if he is innocent, he previously admitted guilt. 37
Admissibility of Expert Testimony
It is clear that psychological assessment is potentially of great importance in
determining the voluntariness or reliability of a confession. An intellectual
assessment revealing significant mental retardation, for example, may show
that the defendant could not have understood his Miranda rights and therefore
could not have waived them ‘knowingly’. Additionally, the tests devised by
Grisso (1998b) can be used for this purpose. Findings of unusual levels of suggestibility
or compliance may support an argument that the police conduct was
coercive in relation to that defendant. An argument that the confession is false
or untrustworthy is, of course, immensely strengthened by expert testimony on
the phenomenon of false confessions and psychological vulnerability.
In seeking to introduce at trial the findings of an expert to demonstrate that a
confession is involuntary or unreliable, the defence must satisfy the evidentiary
requirements of admissibility. Although there are two distinct standards that
American courts apply to specialized expert testimony, depending on the jurisdiction,
all courts require a showing that the proffered evidence is relevant, the
expert qualified and the findings not based on ‘junk science’. American courts
have traditionally distrusted expert testimony as invading the province of the
jury by assessing the credibility of witnesses, usurping the court’s function by
offering a legal conclusion, or claiming an ‘aura of special reliability’ in matters
that a jury could determine from its own experience. 38 These arguments
are frequently brought against the admissibility of false confession testimony.
Although there is not yet a large body of case law about its admissibility, Agar
(1999), Imwinkelried (1999) and Shuman and Sales (1999) provide an overview
of some of the recent appellate cases.
The Frye Standard
Until fairly recently, most courts have admitted novel scientific evidence only if
it could be demonstrated to be based on a theory ‘sufficiently established to have
gained general acceptance in the particular field to which it belongs’. 39 This test,
known as the Frye standard, is still used by several major jurisdictions including
36 Arizona v. Fulminante, 499 US 279 (1991).
37 Crane v. Kentucky, 476 US 688, 689 (1986).
38 Weinstein on Evidence §§702.02, 704.04 [2][c] West 1998.
39 Frye v. United States, 293 F. 1013, 1014 (D.C. Cir. 1923).