A Scientific Protocol for Assessing Witness Credibility in Judicial Contexts
Introduction
In the pursuit of justice, courts often rely heavily on testimonial evidence provided by victims and witnesses. However, the reliability of such statements is influenced by a complex interplay of cognitive, emotional, and contextual factors. Recognizing the limitations of traditional credibility assessment methods, Spanish forensic psychologists Antonio L. Manzanero and José L. González developed the HELPT protocol—Holistic Evaluation of Legal and Psychological Testimony—as a scientifically grounded framework for evaluating testimonial evidence in legal proceedings.
HELPT is a procedure for the collection and assessment of testimonial evidence through a holistic approach (H), which considers the multiple factors influencing witness statements and identifications. It focuses on evaluation (E) of statements and identifications, applied within the legal (L) and criminal procedural context, grounded in psychological (P) principles—particularly those from the psychology of testimony—and primarily aimed at the analysis of testimony (T).
The fundamental objective of HELPT is the application of the scientific method to the collection and assessment of testimonial evidence. One of its core components is the formulation and falsification of hypotheses regarding the possible origin of a testimony, allowing for a structured and objective analysis of credibility.
Historical Development and Theoretical Foundations
The HELPT model is the culmination of decades of research in forensic psychology. As early as the 1990s (Manzanero, 1991; Manzanero & Diges, 1993), it was proposed that credibility assessment in criminal investigations should adopt a general, multidimensional approach to testimonial evidence.
This framework was expanded in later studies, which emphasized the importance of analyzing the factors that influence the accuracy of statements, rather than merely detecting credibility indicators. These influencing factors were grouped into:
- Encoding-related factors (e.g., attention, perception, stress)
- Retention and retrieval factors (e.g., memory decay, suggestibility)
Scientific research has consistently shown that the mere presence of so-called credibility criteria—such as consistency or emotional expression—is insufficient to reliably distinguish truthful from false statements (e.g., Vrij, 2005; Aamodt & Custer, 2006). This evidence underscored the need for a more comprehensive and empirically supported method.
In 2001, Manzanero proposed a specific evaluation method that included not only the analysis of influencing factors but also the comparison of the statement under review with another of known origin. This comparative approach added a new layer of analytical rigor. By 2010, practical forensic work and empirical studies led to the development of a broader credibility assessment procedure that integrated previous models (e.g., SVA, proposed by Steller and Köhnken in 1989, and later revised by Volbert and Steller in 2014, as well as by Köhnken, Scott, and Manzanero in 2015) and introduced new guidelines for evaluating suspect identification evidence—an area previously neglected. It also incorporated a model for assessing testimonial competence (CAPALIST), providing valuable insight into the cognitive and contextual factors affecting witness reliability.
Structure of the HELPT Protocol
HELPT is divided into two main domains: statement evaluation and identification evaluation, each comprising several phases designed to minimize interference and maximize the reliability of the information obtained.
A. Statement Evaluation
Analysis of Influencing Factors
- Event-related
- Witness-related
- System-related (e.g., investigative procedures)
Assessment of Competence to Testify and Prior Knowledge
Statement Collection
- Interview preparation
- Information gathering
Statement Analysis
- Characteristics (how the statement is delivered)
- Comparative analysis with known-origin statements
- Justification based on influencing factors
- Content (what is reported)
- Relation to evidence, context, motivation, and other sources
- Hypothesis formulation
- Definition, falsification, and confirmation
- Characteristics (how the statement is delivered)
B. Identification Evaluation
Assessment of Competence to Identify
Analysis of Event and Witness Factors
Description Collection
- Interview preparation
- Information gathering
- Memory aids
Composite Sketch (if necessary)
Identification Procedure
- Format
- Composition
- Presentation method
- Instructions
Identification Analysis
- Current indicators: bias, confidence, response type
- Post-identification indicators: lineup size, response bias, discriminability
Evaluation of Identification Validity
- Evidence
- Motivation to identify (secondary gain)
- Other information
Possible Causes of False Identifications
Legal Relevance and Application
HELPT is not designed to issue verdicts. Rather, it provides scientifically rigorous information that helps judges and legal professionals assess the honesty and accuracy of witness statements. By integrating psychological principles with legal standards, HELPT enhances the probative value of testimonial evidence and supports fair, informed decision-making.
Its application is particularly critical in cases where testimonial evidence is the primary or sole source of information. HELPT offers a structured method to reduce bias, improve reliability, and ensure that justice is based on the most accurate and contextually informed interpretation of human memory.
Conclusion
HELPT represents a major advancement in the forensic evaluation of testimony. By adopting a holistic, multidisciplinary approach, it bridges the gap between psychological science and legal practice. For jurists, understanding and applying HELPT can lead to more equitable decisions—especially in cases where the truth depends on the credibility of human memory.
References
González, J. L. & Manzanero, A. L. (2018). Obtención y valoración del testimonio. Protocolo Holístico de Evaluación de la Prueba Testifical (HELPT). Madrid: Pirámide.
Manzanero, A. L. & González, J. L. (2015). A holistic model for the evaluation of the testimony (HELPT). Papeles del Psicólogo, 36(2), 125-138. https://www.papelesdelpsicologo.es/English/2568.pdf