Forensic Psychology For Dummies (24 page)
Read Forensic Psychology For Dummies Online
Authors: David Canter
Courts differ on what expert evidence they accept
In one case in England, a man was charged with the murder of his wife, even though a suicide note was found. The court didn’t allow any psychological evidence to be presented about the mental state of the deceased wife. As a result, no discussion was allowed in court about whether she may have been depressed and likely to take her own life, which weakened the case of the accused considerably. In a case in Northern Ireland, a man charged with the murder of his son, wife and daughter claimed that his son had gone berserk and killed his mother and sister (the defendant’s wife and daughter) before killing himself. In this case, psychological evidence was allowed that suggested the deaths were the result of a carefully planned execution by the father. In both cases, the men were convicted of the murders.
In inquisitorial systems, therefore, experts are often given more free rein than in the adversarial system in front of a jury, including civil and quasi-legal processes where judgements aren’t so much about guilt and sentencing but more aimed towards determining solutions in disputes. These variations between courts and legal systems also help to explain why expert forensic psychology evidence can play a significant role in one place but never get a look-in somewhere else, say in a different state or a different country. The matter is complicated further (as it so often seems to be with legal matters) by what any particular court regards as expertise, something I explore in the next section.
Using Your Experience and Knowledge: What Is an Expert Witness?
When experts (such as forensic psychologists) appear in court proceedings, in essence they’re witnesses like any others. They take an oath to tell the truth and are bound to honour the court and its procedures. One crucial exception, however, distinguishes experts from other witnesses. Experts are allowed to give opinions whereas other witnesses can only provide an account of the facts as they know them. Experts have to defend their opinions and explain the basis on which they reach them. They’re closely examined on whether they really do have the expertise to offer the opinions they present in court.
Experts, however, can’t offer an opinion on just anything they happen to know about. What they comment on has to be something that the judge or jury can’t know themselves.
This reality was brought home to me in a case concerning the likelihood that a victim committed suicide, the implication being, of course, that if she didn’t, she was murdered. The victim hadn’t given any overt indication that she intended to kill herself, but I knew of a number of cases of irrefutable suicide in which the person gave no prior hints of wanting to end their life. I thought that this knowledge was relevant to the court, but the judge ruled that a jury of ordinary people would have enough experience in their daily lives to make their own mind up from witnesses about the character of the deceased as to whether she’d intended to kill herself or not. So I wasn’t allowed to provide evidence on this aspect.
Being called as an expert in criminal proceedings
Here’s a summary of some criteria to be met for expert testimony to be admissible in court:
The subject matter must be something a typical juror (or judge) would not usually know about or understand.
Although the defence and prosecution lawyers argue about the expert evidence when presented, the judge decides whether the court accepts the expert opinion at all. He decides whether it provides information distinct from what the jury already knows and is of sufficient reliability and relevance to the case.
A particularly tricky decision for the judge is to weigh up the value of the offered expert evidence (known as its
probative values
) against how damaging it may be to the defendant (known as its
prejudicial value
). For example, if the evidence is of only marginal probative value but may be very detrimental, a judge won’t allow it. How valuable expert testimony is also depends on how well-founded it is.
As a consequence, a key pointer in determining the acceptability of expert evidence is the notion of
reliability.
In other words, is what the expert offers expertise or just opinion? Various legal guidelines on this aspect have emerged over the years, as I discuss in the following sections.
US rulings
The US legal profession features rather more formal guidelines than other countries, which emerge from previous court decisions. Very significant as regards expert witnesses is a 1923 case (
Frye versus United States
) in which a man accused of murder wanted to bring evidence from a polygraph (lie detector) test (which I discuss in Chapter 5) to show he was telling the truth. But the court didn’t allow that evidence to be presented. The ruling in that case on the inadmissibility of the polygraph evidence became the formal statement of what constitutes expert evidence:
The rule is that the opinions of experts or skilled witnesses are admissible in evidence in those cases in which the matter of inquiry is such that inexperienced persons are unlikely to prove capable of forming a correct judgment upon it, for the reason that the subject matter so far partakes of a science, art, or trade as to require a previous habit or experience or study in it, in order to acquire a knowledge of it. When the question involved does not lie within the range of common experience or common knowledge, but requires special experience or special knowledge, then the opinions of witnesses skilled in that particular science, art, or trade to which the question relates are admissible in evidence.
One curious aspect of this clarification is that the ‘expert’ under this ruling doesn’t need to have any special qualifications to offer an opinion, just experience or knowledge not normally available to other people. This means, for example, that a police officer who has arrested many people for the possession of drugs can offer an opinion on whether the quantity of drugs found on a particular person is likely to be for personal use only or is so much that they’re for sale, making the person likely to be a supplier rather than just a user.