What is an expert witness?

Ordinary witnesses typically refer to lay people who saw or experienced a particular event (these are the types of witnesses we have discussed in previous units/modules). An example might include someone going for a walk who witnessed someone breaking into a house along their route.

A professional witness is not someone who can bear witness to an event, but can bear witness to someone's character (Davies & Beech, 2017) – for example, a parole officer, doctor or forensic psychologist may be able to provide information related to an offender's wellbeing, risk or recidivism, which may impact things such as sentencing options and/or treatment.

Expert witnesses, on the other hand, are independent of any event or specific individual, and instead bear witness on the research base surrounding a topic or case (Davies & Beech, 2017). The Criminal Prosecution Service (CPS, 2021) describes an expert witness as "a person whose evidence is intended to be tendered before a court and who has relevant skill or knowledge achieved through research, experience or professional application within a specific field sufficient to entitle them to give evidence of their opinion and upon which the court may require independent, impartial assistance ". To put it simply, they are experts in a particular field and are called upon to provide their expertise to help guide criminal justice processes. For example, if evidence or a confession is thought to have been coerced from a defendant by police officers, then an expert in the field of false confessions and police coercion may be called in to discuss how this occurs – based on this expert testimony, certain evidence may be considered no longer admissible and/or jurors may alter their verdicts based on this information. After the witness has given their report, they will then have to provide a written summary with a conclusion to the court, covering what was said, who carried out any examinations and the literature that was used.

Forensic psychologists may be called upon to provide expert testimony in many different areas (Davies & Beech, 2017), such as:

• a defendant's mental capacity, which may impact their ability to understand court proceedings and their fitness to plea - this may be one of the most common areas where a forensic psychologist may be retained, and they can implement psychometric and assessment tools to identify a defendant's clinical profile and how it may have impacted their behaviour or their understanding of the case. If a defendant is found unfit to plea, the case becomes a trial of the 'facts', whereby only hard evidence is deliberated rather than the psychology of the defendant, and it can also change sentencing options (e.g. defendants found guilty may instead be admitted to a hospital or given a community supervision licence)
• alternative explanations for a defendant's actions (e.g. individual, emotional or cognitive explanations)
• mental health conditions and how they may impact victimisation and/or offending behaviour
• how victims may behave following an offence
• offender risk assessments and likelihood of harm/recidivism
• the use of psychometric testing to understand offending behaviour and the validity of psychometric testing
• the impact of court processes on family, children and vulnerable individuals
• how memory works and how it may be impacted by police or court proceedings
• they may even be called to provide their expert opinion on other expert witnesses