There must be sufficient copies of the expert report at court and the expert should bring any notebooks containing background calculations which have not been appended to the report. The expert may refer to these to refresh his/her memory, if necessary.
The expert will normally be able to remain in court before and after giving evidence. It is for the procurator fiscal tom decide whether they wish the expert to remain in court and seek the court’s permission, to defence will be able to object to any request for the expert to remain in court. Similarly the defence experts may be given leave to remain in court.
While in court, the expert should make a note of the evidence and, in particular, whether witnesses have given evidence which lays the factual basis for his/her evidence. If they have not, the expert should draw this to the attention of the fiscal.
When the expert gives evidence, s/he should speak clearly and slowly, watching the sheriff’s/Judge’s pen to ensure the bench is keeping pace with the. As with all witnesses, experts should ensure that they understand the questions and, if possible, finish their answers. They should try to keep their replies short. Once they have taken the oath, they should not discuss their evidence with anyone until they have finished giving evidence. In exceptional circumstances, the court may give permission to discuss matters about which the expert has not yet given evidence, if the procurator fiscal requires clarification.
The expert may draw on the work of others in his/her field of expertise as part of the process of reaching a conclusion, provided that s/he refers to that material in his/her evidence.
As a general rule, where the issue before the court involves matters other than the purely scientific, the expert should confine him/herself to the latter and avoid opinion on the legal or general merits of the case unless specifically asked. In those circumstances, the expert may, if s/he also observed the facts, be asked the very questions the jury has to decide (see also The report on giving an opinion on such questions in the report). If the expert’s opinion is based on the facts proved by others, it is for them to give evidence of those facts. The court may put those facts to the expert hypothetically and ask him/her to give an opinion of them.
Although the normal rules of hearsay apply, there are a number of exceptions specifically relevant to expert evidence. An expert giving evidence in proceedings may base an opinion on, or make an inference from, a statement and any evidence s/he gives based on that statement will be treated as evidence of what it states, provided:
- The statement was prepared for the purposes of criminal proceedings or a criminal investigation; and
- The person who prepared the statement had, or may be reasonably supposed to have had, personal knowledge of the matters stated in it.
Once the expert has taken the oath, the procurator fiscal will ask him/her to give evidence of his/her experience and qualifications. This is to establish the witness’s status as an expert, so that s/he will be permitted to give opinion evidence, and to persuade the court to attach more weight to his/her evidence than to that of the defence expert.
The fiscal will often lead this preliminary part of the expert’s evidence, reading out the expert’s CV and asking him/her to confirm that it is correct. The defence may then cross-examine on the qualifications, even before the expert has given the substance of his/her evidence, in order to suggest that s/he is not sufficiently qualified or experienced to be regarded by the court as an expert.
Whether a witness is competent to give evidence as an expert is a matter for the court to determine. When a court is presented with the conflicting opinions of more than one expert and must decide on whom to place greater reliance, one of the relevant factors may well be a comparison of the relative experience and qualifications of experts, as well as their general credibility.
The expert should first be asked to give evidence of the facts upon which his/her opinion is based.
The expert may introduce evidence on video, but any existing commentary is usually turned down and s/he must explain what the video shows and its relevance. The expert should accompany the court on any site visit and, if asked, explain what happened.
If asked a question that is not within the expert’s field of expertise, s/he should tell the court. S/he may explain why it is not relevant and the prosecutor may state that another witness is available who can deal with the matter.
The defence will be taken to have accepted the expert’s evidence if they do not cross-examine him/her with a view to casting reasonable doubt on his/her opinions, or at least indicate that the evidence given is not accepted. If the defence seeks to cut short any of the expert’s answers, the court should be asked to allow the expert to finish. The court may exclude questions it considers improper or offensive.
The object of cross-examination is to:
- weaken, qualify or destroy the prosecution case. This can be done by attacking the veracity or expertise of the expert, or by seeking to get the expert to contradict or qualify his/her evidence. The expert should be alert to questions which try to lead him/her into giving an opinion on matters outside his/her field of expertise; and
- establish the defence's case by bringing out evidence which supports it.
The expert should do his/her best to answer a question, rather than try to second-guess or anticipate what is behind it. S/he should try to answer in his/her own words, rather than adopting those used by the defence advocate, and should avoid any invitation to speculate.
This is confined to an explanation of matters arising out of cross-examination, and no new facts may be introduced without the leave of the court. Leading questions are generally not allowed.
Where the defence calls an expert and there is a conflict in evidence, that expert’s competence should, if appropriate, be challenged by questions regarding training and experience. The procurator fiscal should discuss with the prosecution expert before trial appropriate questions for cross-examination. While the defence expert is giving evidence, the prosecution expert may be allowed to sit it near the fiscal to assist with questions.