Evidence Law in Mexico

Introduction

Mexican evidence law has been fundamentally shaped by the 2008 criminal procedure reform, which transitioned the system from an inquisitorial written model to an accusatorial adversarial model. The National Code of Criminal Procedure (CNPP, 2014) establishes a comprehensive framework for the admission, presentation, and evaluation of evidence in criminal proceedings. Civil evidence is governed by the Federal Civil Procedure Code and state procedural codes, with varying standards across jurisdictions.

Sources of Evidence Law

Criminal evidence is primarily governed by the CNPP, which adopts principles of orality, immediacy, contradiction, concentration, and continuity. Civil evidence is governed by the Code of Commerce (for commercial matters) and the Federal Code of Civil Procedure (for federal civil matters), with state codes governing ordinary civil litigation. The SCJN’s binding precedents (jurisprudencia) on evidentiary issues ensure uniform interpretation of constitutional evidentiary standards.

Burden of Proof

In criminal proceedings, the burden of proof lies with the prosecution (Ministerio Público), which must prove guilt beyond a reasonable doubt. The presumption of innocence (Article 20 of the Constitution) requires acquittal if reasonable doubt exists. In civil proceedings, the plaintiff bears the burden of proving the facts constituting their claim, while the defendant bears the burden of proving affirmative defenses. Proof standards include preponderance of the evidence and clear and convincing evidence depending on the nature of the proceeding.

Types of Evidence

The CNPP recognizes several categories of evidence: testimony (testimonial), expert evidence (pericial), documentary evidence (documental), material evidence (material), and demonstrative evidence (demostrativa). Expert testimony is particularly important in complex criminal cases, with experts appointed by the parties or, in some cases, by the court. Documentary evidence includes both public and private documents, with public documents having formal evidentiary value (valor probatorio pleno).

Oral Trial Evidence

The oral trial (juicio oral) is the central evidentiary event in the accusatorial system. Evidence is presented directly before the trial judge, with witnesses subject to direct examination and cross-examination. Hearsay is generally inadmissible, and prior written statements may be used only for impeachment purposes. The principle of immediacy requires that the trial judge personally observe the presentation of evidence.

Conclusion

Mexican evidence law has undergone a profound transformation with the adoption of the adversarial system in criminal proceedings. The emphasis on oral evidence, cross-examination, and judicial immediacy has strengthened procedural fairness. Civil evidence law continues to evolve, with ongoing efforts toward harmonization through the National Code of Civil Procedure.