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Article 588 bis a of the LECrim establishes that the adoption of technological investigation measures must adhere to the principles of specificity, suitability, exceptionality, necessity, and proportionality. First, specificity implies that the measure must be directly related to the investigation of a serious crime and cannot be applied indiscriminately. Suitability requires that the measure be the most appropriate to achieve the investigation’s objective, considering less intrusive alternatives. Exceptionality indicates that these techniques should only be used when no other viable options exist for obtaining evidence. Necessity requires that their application be justified in the judicial request, demonstrating that no other means are available. Finally, proportionality obliges an assessment of whether the severity of the investigated crime justifies the impact on the fundamental rights of the investigated party.
Moreover, prior judicial authorization is essential for adopting these measures. The judge must base their decision on solid indications of the commission of the crime and the necessity of the measure for the success of the investigation, preventing arbitrary violations of fundamental rights.
The LECrim establishes various technological investigation measures, each with specific requirements and safeguards. Among them is the interception of telephone and telematic communications, regulated in Article 588 ter a and following, which allows for the interception of calls and messages with judicial authorization. This is an essential tool in investigations related to terrorism, organized crime, and crimes against state security. Another significant measure is the capture and recording of oral communications through electronic devices, regulated in Article 588 quater a and following, which permits the installation of devices in private places to record suspects' conversations, provided there is judicial authorization based on solid indications.
Additionally, Article 588 quinquies a and following regulate the use of tracking and geolocation devices, allowing for the deployment of geolocation systems in vehicles or belongings of investigated individuals. This mechanism facilitates discreet monitoring of their movements. The search of devices and computer equipment, established in Article 588 septies a and following, details the conditions under which computers and other electronic devices may be examined, ensuring the privacy of data unrelated to the investigation. Finally, technological assurance measures, provided in Article 588 octies a and following, contemplate the blocking of devices or the preservation of electronic data to ensure their availability in criminal proceedings.
All these measures are subject to rigorous judicial and procedural controls to ensure their application complies with the legal and constitutional framework.
The Attorney General’s Office has issued several circulars establishing interpretative criteria on these measures. Among them, Circular 1/2019 addresses common provisions and assurance measures, while Circular 2/2019 elaborates on the interception of telephone and telematic communications. Circular 3/2019 focuses on the capture and recording of oral communications, Circular 4/2019 analyzes the use of technical imaging, tracking, and geolocation devices, and Circular 5/2019 regulates the search of devices and computer equipment. These circulars constitute a doctrinal framework guiding legal practitioners in the application of these measures, ensuring a uniform interpretation that respects fundamental rights.
Supreme Court Judgment 133/2025, of February 19, has been a milestone in the interpretation of technological investigation measures. In this ruling, the Supreme Court analyzes prior judicial authorization, emphasizing that any intervention in electronic devices must be supported by a reasoned judicial decision specifying the investigated facts, the necessity of the measure, and its proportionality. Furthermore, the ruling highlights the importance of clearly delineating the scope of the measure, avoiding generic interception orders, and ensuring that the duration, investigated subjects, and intercepted means are precisely specified.
Another relevant aspect addressed in this ruling concerns the principle of proportionality. The Supreme Court stresses the need to assess whether the benefit obtained through the measure outweighs the harm to the investigated person’s privacy. In the specific case analyzed, the Court declared null and void a piece of evidence obtained through an excessively broad interception, reinforcing the requirement for strict control over these measures. The Supreme Court also refers to European regulations, aligning with the case law of the European Court of Human Rights. According to this doctrine, any interference with privacy must be prescribed by law, serve a legitimate aim, and be necessary in a democratic society.
The incorporation of technological investigation measures into the LECrim represents progress in adapting criminal proceedings to the digital age. However, their application must be subject to strict controls to ensure their proper and proportional use. Jurisprudence and the Attorney General’s Office guidelines play a key role in the interpretation and application of these rules, ensuring that crime prosecution does not compromise citizens’ fundamental rights.
In this context, STS 133/2025 sets an important precedent in consolidating these principles and their practical implementation. Its detailed analysis of the requirements for judicial authorization, the delimitation of the measure’s scope, and proportionality reinforces legal certainty in the use of these tools. The evolution of legislation and case law will continue to be crucial in balancing the effectiveness of criminal investigations with the protection of individual rights in an ever-changing technological landscape.
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