Interviews conducted globally by police and other law enforcement agencies with suspects, victims, and witnesses play a vital role in shaping criminal justice outcomes. Principles and protocols now exist to set a frame and a normative framework to assist investigators and prosecutors.

In 2021, the ‘Principles on Effective Interviewing’ were launched. These Principles were developed by an international team of leading experts to establish, for the first time, a clear set of recommendations and minimum international standards for law enforcement interviewing practices, grounded in science, ethics, and law. They are known as the Méndez Principles, after the UN Special Rapporteur, Professor Juan Méndez. They provide guidance on obtaining accurate and reliable information, respecting the human rights and dignity of all, including through the implementation of legal and procedural safeguards during the first hours of police custody.

Legal and procedural safeguards, rooted in international law, are vital to any interview process. When applied effectively before, during, and after an interview, they uphold human rights and strengthen both the credibility and evidentiary value of the information gathered.

Such safeguards help ensure fair treatment in information-gathering and judicial proceedings, leading to legally sound outcomes. Backed by UN resolutions and EU Directives, they set standards for the arrest, detention, and questioning of suspects, ensuring that ethical and effective interviewing remains protected under international human rights law.

The relevance of the Méndez Principles

The Méndez Principles are highly relevant today because they address a fundamental tension in investigations: obtaining reliable information while fully respecting human rights.

• They reject coercion in favour of science-based interviewing. The principles promote rapport and evidence-led questioning over coercion to obtain more accurate and reliable information.
• They protect human dignity. They ensure suspects and victims are treated respectfully, reducing the risk of abuse, trauma, or wrongful convictions.
• They strengthen legal outcomes. Ethically obtained information is more likely to be admissible in court, avoiding dismissal over procedural violations.
• They support trauma-informed practices. With victims and vulnerable witnesses, the principles promote harm reduction, tailored questioning, and prevention of re-victimization.
• They build trust in justice systems. Transparency and respect for rights boost community cooperation, police legitimacy, and trust in the legal system.
• They address global challenges. The principles provide a universal, adaptable framework that enhances cross-border investigations from counterterrorism to organised crime

In short, the Méndez Principles align ethical duty with investigative effectiveness, making them a blueprint for justice systems that seek truth without compromising on abuse.

There are currently two distinct approaches worldwide. Several member countries are adopting an ethical model known as ‘investigative interviewing,’ designed to gather detailed, reliable information while respecting human rights. For several years, Méndez led a team of legal, forensic psychology, and criminology experts, with civil society representatives, to produce a formal declaration of principles grounded in science, law, and ethics.

However, evidence from research and real cases shows that in many countries, law enforcement remains unfamiliar with the investigative interviewing approach. Instead, unethical practices persist, marked by presuming guilt and pursuing confessions through manipulation, intimidation, or even physical torture, often resulting in miscarriages of justice and failed investigations.

ImpleMéndez COST Action lays out a timely strategy to unite regional and national networks of researchers, practitioners, and policymakers, building on early progress to expand the implementation of the Méndez Principles and end the cruel, inhumane interrogation practices that have harmed countless lives. In numerous countries, the press regularly reports these cases of abuse, excesses, and disrespect for human dignity, regardless of the context.

This is where the network steps in, bringing forward the insights needed to raise awareness of effective interviewing for investigations.

“Undertaking this COST Action has been a richly rewarding experience. We have seen membership numbers increase hugely in just over two years. Members are present in all COST member countries, near neighbour countries, its COST partner countries, and its Cooperating member countries as well. In addition, we have members from 11 international partner countries. All this means that we have members from all parts of the world. Members include those from academia (involving many different fields of study), practice, policymaking and NGOs, This growth has led to the developments of around 30 separate initiatives, where networks of members are involved in scientific studies, design of training materials, policy development, national and regional collaboration, as well as the emergence of Mendez Centres that are designed to sustain the overall goals of ImpleMéndez beyond the life of the COST Action. None of this exciting expansion of interest and involvement of such huge numbers of members would have been possible with COST funding. Such support has enabled the launch of many examples of vibrant activity and networking between people around the globe, who would not have worked together had it not been for the facility that COST provides.” Prof. David Walsh, Chair of ImpleMéndez

Since its launch, ImpleMéndez has gathered over 350 members across 59 countries. The network is developing a strategic framework for investigation transformation (FIT), based on the Méndez Principles, in collaboration with researchers, practitioners, and policymakers, including those from countries that have not yet fully adopted the principles.

ImpleMéndez will create investigative interviewing models tailored to local contexts and cultures without compromising the integrity of the Méndez Principles, while upholding law, ethics, and science. The aim is to improve the results of investigations in full respect of human rights.

Additionally, the network will also promote the establishment of Méndez Centres of Interviewing, advance agreed FIT frameworks for implementing the principles, and provide clear methodologies and tools to support their practical application worldwide.

The ImpleMéndez network strategy focuses on rolling out a tailored Framework for Investigation Transformation (FIT), including mandatory audio and video recording of interviews, the development of training models on effective interviewing, and capacity-building for police, lawyers, and judicial staff. It also seeks to embed a culture of respect for the Méndez Principles across institutions and to establish Méndez Centres of Interviewing.

View the Action webpage

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