I'm not a lawyer, but, I do not believe Harshman can give and "educated opinion" on RA's voice or whether it is a match to the voice on LG's video because he is not credentialed in the field of voice analysis or anything even adjacent to that imo -
"... a medical expert can offer insight into the injuries discussed in the case, while a forensic expert can give an educated opinion of evidence found at the crime scene. Other types of expert witnesses include financial, vocational, ballistics, and mental health experts...."
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2: "Experts are the only witnesses who are allowed to give evidence about their opinions. These may include mechanics, doctors, engineers, appraisers, carpenters, repairmen, psychiatrists, psychologists, or other."