Legal Psychology experts draw upon the scientific knowledge base of fundamental psychological functions (e.g. perception, memory, and decision making) and social dynamics (e.g. compliance and suggestibility) to address forensic questions concerning the validity of statements made by eyewitnesses, victims, and suspects. Their expertise involves how internal (e.g. intoxication) and circumstantial factors (e.g. interrogation techniques) may affect the validity of such statements.
Experts within the field of Legal Psychology chiefly conduct evaluations that fall within the following three subfields:
009.1 The validity of statements
Within this subfield, Legal Psychology experts conduct evaluations on the validity of statements made by victims, suspects, and witnesses (including those made by children and individuals especially vulnerable to suggestion or pressure) for instance allegations of criminal acts, confessions or recanted statements, and descriptions of witnessed events. Experts within this subfield take into account how victims, suspects, and witnesses have been interviewed (including specialized interview methods for children and individuals vulnerable to suggestion or pressure) and how this may affect the quality of their statements. They also look into environmental influences on statements (e.g. perception conditions, imprisonment, sleep deprivation).
009.2 Deception relevant to statements
Within this subfield, experts on Legal Psychology conduct evaluations related to deception detection techniques, including expert opinions on verbal and non-verbal credibility assessment techniques and tests to detect malingering (faking symptoms of illness or disorder) and declared memory dysfunction.
009.3 Psychology of evidence and evidence-gathering
Within this subfield, experts on Legal Psychology try to advise triers of fact by applying principles of psychological decision theory (e.g. the literature on cognitive biases) to evidence (e.g. outcomes of line-ups). Experts within this subfield take into account the reliability and validity of investigative methods. These include identification and identification procedures of persons (e.g. line-ups, show-ups), objects (e.g. evidence line-up) and voices.
Legal Psychology experts also provide second opinion reports on the topics listed above.
Boundaries of the field of expertise
The field of Legal Psychology and the field of 003.0 Forensic Psychiatry and Psychology (FPP) as determined by the Board are different fields of expertise. The core questions answered by experts within the field of Legal Psychology concern the validity of statements, evaluation of deception and the scientific value of evidence.
Experts in Legal Psychology evaluate witness statements, assess deception-detection (tools), and examine cognitive biases in investigative techniques as far as these are relevant to the evidence. In contrast, FPP primarily concerns diagnostic assessment of the psychopathology of the suspect in relation to the alleged crime. FPP expertise assists the judge in answering the third and fourth question raised in article 350 Sv, pertaining to criminal responsibility of the suspect and the determination of sanctions.
Legal Psychology experts, on the other hand, assist the judge in answering a different question, namely the first issue raised in 350 Sv: whether the suspect has committed the alleged crime. Hence, Legal Psychology expertise contributes to fact finding. In doing so, Legal Psychology experts may use information from the field of FPP. For example, when evaluating the value of a confession, Legal Psychology experts may take into account the psychopathology of the suspect.
As another example of the overlapping knowledge base between Legal Psychology and FPP experts, Legal Psychology experts may evaluate witnesses reports of memory loss, thereby relying on psychometric tools for assessing symptom validity (e.g., malingering). In addressing issues of psychopathology and malingering, Legal Psychology experts respect the boundaries of their expertise, which specifically implies that they do not make psychiatric diagnoses.
The field of Legal Psychology as defined by the NRGD is also separate from that of investigative psychologists working in a police context. Although Legal Psychology experts and investigative psychologists may rely on a similar knowledge base, their respective roles within legal proceedings are distinctly different. Investigative psychologists provide advice to law enforcement employees and/or to the prosecutor during the (pre-trial) investigative phase.
Legal Psychologists report to courts of law and are considered experts in terms of the Code of Criminal Procedure.