There is widespread and justified concern about the reliance on expert opinion in law court cases. Where experts disagree on an interpretation of the facts, there is always the possibility that the more charismatic and persuasive expert's opinion will prevail for this reason alone. Their reason for holding the opinions they do could be more to do with their own personal prejudices than their professional expertise. However, if we want justice to be done, we should distinguish sharply between this and expert evidence which is not reliant on interpretation. It would be a tragedy if key advances in tackling crime such as matching DNA were regarded with suspicion just because such evidence came from an expert witness.