They needed no training or expertise. They were simply testifying to the truth. In a court room you have a judge, lawyers, witnesses, and expert witnesses. The judge decides if the lawyer's arguments are compelling and if the witnesses are credible. The lawyer puts all pieces together in a logical, factual, and believable case.
Expert witnesses testify with technical data which can dramatically change the opinion of the judge.
Often they're nervous. Often they're a little scared. Yet, their testimony can convict a murderer or free an innocent person. Without the witnesses there is no case. Most of all they need to hear from witnesses.