An expert witness may be presented by the State or the Defense in a criminal trial. This witness is deemed an “expert” by the Judge, which allows this witness to give opinions or other testimony in any area of scientific, technical, or specialized knowledge.
This scientific, technical, or specialized knowledge testimony or opinion must be such that it could assist the trier of fact (which are the jury members in a jury trial and the judge in a court trial) in understanding the evidence or in determining a fact at issue in the case. This means that the opinion or testimony must be reliable information and not just a “novel idea” that is not approved or accepted by others in the expert witness’s field. The testimony also cannot be common knowledge to where the jury member or trier of fact would have reached the same conclusion given the same evidence in front of them. The expert witness should aid the trier of fact in things they need help with, not confuse them or tell them what they already know.
In determining whether the witness is a sufficient expert for trial, a judge would rely on the Rules of Evidence. In Minnesota, Rule of Evidence 702 gives discretion to the court to make this determination if the witness is an expert based on their specialized knowledge and qualifications and the information they seek to present.