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.
The expert must have the qualifications and experience to be able to give the court assistance.
The expertise must be objectively established and generally accepted by other experts within that area of knowledge.
The value in helping to form an opinion about the evidence must be greater than the likely negative influence on the decision about the defendant.
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
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.
The expert must have the qualifications and experience to be able to give the court assistance.
The expertise must be objectively established and generally accepted by other experts within that area of knowledge.
The value in helping to form an opinion about the evidence must be greater than the likely negative influence on the decision about the defendant.
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
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