Criminal police investigation is the cornerstone of the criminal process in Spain. It is the initial phase that allows the criminal justice system to discover, verify and prosecute committed crimes, while ensuring the constitutional guarantees of those under investigation and the protection of victims.
Below, we examine in detail how this investigation is structured, from the crime scene to the judicial validation of evidence, including the actions of the Judicial Police, the police report, the chain of custody and legal limits.
How does a criminal police investigation begin?
Every criminal investigation begins with the existence of rational indications of criminality. Police actions can be triggered by a complaint, emergency call, direct knowledge of the facts or anonymous information. The Judicial Police acts in accordance with articles 282 and following of the Criminal Procedure Law (LECrim), in coordination with the Public Prosecutor’s Office and the investigating judge.
Phases of criminal police investigation
Intervention at the scene of the events (crime scene)
The Police must:
- Secure the scene to prevent evidence contamination.
- Cordon off and preserve evidence.
- Document and photograph the scene.
- Prepare the corresponding report and include it in the police file.
Crime scene in violent crimes
This type of intervention is co
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Why is it so important to respect the chain of custody during criminal investigation?
The chain of custody is fundamental during criminal investigation because it guarantees the authenticity, integrity and reliability of the traces, objects and evidence collected. Respecting it is not a formality, but an essential requirement for expert evidence derived from such traces to be validly assessed at trial. I detail it legally:
Preserves the identity of the object
It allows demonstrating that what is analyzed is the same as what was collected, without alterations, substitutions or contamination. This identity is a basic requirement for the evidence to be legitimate.
Ensures authenticity and legitimacy of evidence
The chain of custody «serves as a formal guarantee of the authenticity and integrity of expert evidence.» It is not evidence itself, but its breach can compromise the credibility of the expert result.
Protects the right to due process (art. 24.2 CE)
A serious breach of the chain can constitute a violation of the fundamental right to due process, by introducing uncertainty about the prosecution evidence. In this regard, the Supreme Court has warned that a significant break could determine its exclusion as valid evidence.
Avoids nullity or loss of probative value
Although a breach does not i
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Legal limits of criminal investigation: rights of the person under investigation
Criminal investigation cannot be conducted without restrictions. In a Rule of Law, obtaining evidence must respect the fundamental rights of the person under investigation, in accordance with article 24 of the Spanish Constitution. Evidence obtained through violation of these rights may be declared null by the courts, having been obtained in breach of procedural guarantees.
Right to remain silent and not to confess guilt
The detainee has the right to remain silent, to not testify against themselves and to not confess guilt. These guarantees are enshrined both in article 520.2 of the LECrim and in articles 6 ECHR and 14 ICCPR.
Right to legal assistance
From the first moment of detention, the person under investigation has the right to be assisted by a lawyer. This assistance is not limited to their physical presence, but includes the right to receive clear, immediate and understandable information about the facts they are accused of. The Constitutional Court has reinforced this guarantee in judgments where it emphasizes that the right of defense requires access to the essential elements of the police report before any interrogation.
Right to access the essential content of the police report
Although full access to the police report at the police station is not recognized, the lawyer has the right to know the essential elements to challenge the legality of the detention, such as:
Abogado penalista en Madrid (Graduado en Derecho y ADE con Máster de Acceso a la Abogacía), experto en procedimientos complejos y técnicos en Derecho Penal. Cuenta con títulos como el Curso de DerechoPenal Avanzado impartido por magistrados del Tribunal Supremo en el Iltre. Colegio de Abogacía de Madrid.