An expert witness is someone who is asked to assist in the proceedings when specialised 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 explain the injuries suffered by the victim
and how they were inflicted, or for a psychologist or psychiatrist to describe the psychological characteristics of the defendant
in order to conduct a personality evaluation, or for a computer engineer to show how a software programme was used in committing the crime. In these cases, the doctor, psychologist or computer engineer use their technical and scientific knowledge to provide a better understanding of what happened.
The assistance of expert witnesses is requested by the judge
or the Public Prosecution Service
, either on their own initiative or because one of the participants in the proceedings has requested it, and they receive a fee.
Expert witnesses first conduct any necessary tests and then write a report with their conclusions about what they examined and assessed
. If an expert witness is called to appear at the trial
, they will testify and answer questions on the tests done and the conclusions drawn from them.