This report provides a systematic analysis of the legal assessment of evidence in cross-border cases, demonstrating why materials obtained through international cooperation channels cannot be automatically treated as admissible and reliable. It examines the core international mechanisms for obtaining and transferring evidence: the 1970 Hague Evidence Convention for civil and commercial matters, mutual legal assistance under the UN Convention against Transnational Organized Crime, the European Investigation Order within the EU, and the Second Additional Protocol to the Budapest Convention for electronic evidence. Key assessment criteria are explored in detail: lawfulness of acquisition, provenance, integrity, completeness, disclosure, challengeability, translation, and parallel use across multiple jurisdictions. Special attention is given to the procedural safeguards of the defense — equality of arms, adversarial proceedings, access to originals and metadata, and the right to counter-expertise — in the context of Article 14 ICCPR and OHCHR fair trial standards. The author proposes a practical defense model based on forensic mapping of the evidentiary chain and shifting the dispute from the content of the evidence to its route and procedural integrity.