When can Laboratory Criminalists give Opinion Evidence?
Lay witnesses in any court of law are, in most cases, not required to give any conclusions, inferences, or opinions, because this is the duty of the jury (Capellino, 2020). But in cases where the jury is unable to draw conclusions from the evidence provided, experts such as laboratory criminalists may be called to give their expert evidence or opinion evidence. Opinion evidence describes evidence that witnesses give based on what they believe, think, or infer. When laboratory criminalists are called to give evidence in court, they are expected to give expert evidence based on their special knowledge obtained through work experience, training, or education (Capellino, 2020). For laboratory criminalists to give their evidence as experts, they must have the following background:
- They must have sufficient technical, scientific, and other specialized knowledge, which will help a trier of opinions to not just determine facts in the issue but also understand the evidence.
- They must have sufficient data and facts with which to back up their opinion.
- They must have reliable methods and principles upon which to base their opinions.
- They must have previously applied the methods and the principles to similar cases before.
According to Family Law (n.d.), for experts to give testimony in the form of opinions, or for them to give evidence, not as experts, then their evidence is limited to the following:
- Their testimony must be based on their rational perceptions.
- Their testimony should be helpful in understanding evidence or determining facts in the case.
- Their testimony should not be based on technical, scientific, or any specialized knowledge.
For laboratory criminalists to give evidence in the form of opinions, then their evidence must be based on:
- What they learned or saw directly
- Information that they got heard, or received from other people.
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