DNA and Criminal Evidence: The Court of Cassation Reaffirms the Importance of Scientific Protocols (Judgment no. 26031/2025)

In the landscape of modern criminal law, DNA evidence represents one of the most powerful and, at the same time, most delicate investigative tools. Its ability to identify individuals with a very high degree of accuracy often makes it decisive in trials. However, its inherent strength also demands strict adherence to scientific procedures and protocols, without which its very reliability could be compromised. It is precisely on this crucial point that the Supreme Court of Cassation has expressed itself with the recent Judgment no. 26031 of July 15, 2025, offering a fundamental clarification on the conditions for the validity and appreciation of genetic investigations.

The Reliability of DNA Evidence and its Limits

The case under examination, which involved the defendant S. T., concerned genetic investigations carried out on zip ties found at the scene of a robbery and used to restrain the victim. The central issue brought before the judges was the admissibility and evidentiary value of such analyses, in light of alleged violations of international scientific protocols. DNA evidence is a cornerstone of modern investigations, but its validity is never absolute; it is intrinsically linked to the correctness of the procedures by which it is acquired, preserved, and examined. The judgment in question reminds us that even the most advanced science must adhere to the rules of law, especially when personal liberty is at stake.

In the context of genetic investigations, comparative DNA analysis conducted in violation of the procedural rules prescribed by international scientific Protocols regarding the collection and preservation of the materials to be examined, as well as the repetition of analyses, deprives the outcomes of certainty, thus making it impossible to attribute any evidentiary value to them. Such analysis constitutes, rather, a mere procedural datum, devoid of independent demonstrative capacity and subject to appreciation only as a potential confirmation of other evidentiary elements. (Case relating to genetic investigations on zip ties found at the scene of a robbery and used to restrain the victim).

The maxim of Judgment no. 26031/2025 is extremely clear and impactful. The Court of Cassation, presided over by A. P. and with A. M. D. S. as rapporteur, unequivocally states that if the DNA analysis does not comply with the "international scientific Protocols" – which concern the "collection and preservation of the materials to be examined" and the "repetition of analyses" – its outcomes are deprived of "certainty." This means that such evidence can no longer be considered independent evidence, but is reduced to a "mere procedural datum," without its own "demonstrative capacity." In practice, without adherence to these safeguards, genetic analysis can only "confirm" other already acquired evidentiary elements, and cannot form the sole or primary basis for a conviction. This principle is crucial for the protection of the defendant's rights and for the correctness of criminal proceedings, drawing attention to Article 192 of the Code of Criminal Procedure, which requires the judge to evaluate evidence by accounting for the acquired results and the criteria adopted.

International Scientific Protocols: A Safeguard of Guarantee

But what are these "international scientific Protocols" and why are they so important? They represent a set of guidelines and technical standards developed by the scientific community to ensure the maximum reliability and reproducibility of genetic analyses. These protocols cover every phase of the investigation, from sample collection at the crime scene (collection), to its preservation in conditions that prevent contamination or degradation, up to the analysis methodologies and the possibility of repeating the tests to verify their accuracy. Their violation can lead to:

• **Sample Contamination:** The presence of foreign DNA that can falsify results.
• **Degradation of Genetic Material:** Improper preservation can render the analysis impossible or unreliable.
• **Analysis Errors:** Non-standardized procedures can lead to incorrect interpretations.
• **Impossibility of Verification:** The absence of protocols or their violation can prevent the defense from replicating the analyses and contesting the results, violating the right to adversarial proceedings (Articles 359 and 360 of the Code of Criminal Procedure concerning unrepeatable technical assessments).

The Court of Cassation, by annulling with referral the decision of the Court of Review of Rome, intended to emphasize that the validity of scientific evidence is not solely based on its nature, but on its conformity to the rules that guarantee its objectivity and verifiability. A DNA analysis performed in a non-compliant manner is, in fact, a "crippled" analysis, lacking the robustness necessary to support a conviction.

Implications of the Judgment: Certainty vs. Mere Procedural Datum

The distinction between "evidentiary value" and "mere procedural datum" is at the heart of the ruling. An indication, according to Article 192, paragraph 2, of the Code of Criminal Procedure, can form the basis of proof of responsibility only if it is "serious, precise, and consistent." If the DNA analysis does not comply with the protocols, it loses its "precision" and "seriousness," degrading to a simple element that needs to be corroborated by other solid and independent evidence. It can no longer be the "engine" of the prosecution, but only a "passenger" confirming a path already traced by other elements. This decision reinforces the need for continuous training for legal professionals and forensic technicians, so that genetic investigations are always conducted in full compliance with best scientific practices and procedural guarantees. Only in this way can science be a true ally of justice, without compromising the fundamental principles of our legal system.

Conclusions

Judgment no. 26031 of 2025 by the Court of Cassation represents an important warning for all those operating in the field of criminal justice. It reiterates that scientific evidence, however advanced, is not exempt from rigorous scrutiny of its formation. Adherence to international scientific protocols is not a mere technicality, but an essential guarantee for the certainty of outcomes and for the protection of fundamental rights. In an era where technology is advancing by leaps and bounds, it is crucial that the law maintains firm principles of reliability, transparency, and adversarial proceedings, ensuring that every piece of evidence is not only powerful but also unassailable in its origin and execution.