Hi Katriona,
What evidence do you have that the professional witness' conclusion is clearly wrong?
For the evidence to influence the jury, it will have been assessed by the judge presiding over the trial that:
- The expert witness is qualified to give their opinion on the matter;
- The expert witness is credible (i.e their are clearly biased);
- The opinion given by the expert witness is reliable (including an analysis of the type of expert evidence given, the conclusion drawn, the methodology used in coming to this conclusion, any other explanations for the result apart from the conclusion, how established is the field of study)
Any expert witness called by the prosecution (or police) can be cross examined by the defence. Therefore, what happened during cross-examination?
If you believe this opinion should not have been admitted into court, or that the jury was incorrectly/inadequately directed by the judge in relation to the evidence (based on law, not on your own opinions) then the defendant can lodge an appeal based on this ground. However, the error must be materially significant, in that, the error could have changed the outcome of the trial (conviction) or sentence. This is the best way to challenge the evidence of an expert. One cannot sue the expert who gives evidence.
The defendant can bring a negligence action against his representative (or lawyer) for failing to follow his instructions