Experts and specialists are someone who is asked to assist in the proceedings when specialized technical, scientific or artistic knowledge is necessary to understand the facts or weigh up the evidence. For example, it may be necessary to have a doctor to explain the injuries suffered by the victim and how they were inflicted, or a psychologist or psychiatrist to describe the psychological characteristics of the defendant in order to conduct a personality evaluation, or a computer engineer to show how a software program was used in committing the crime.