What Does an Investigating Judge Do & When Do They Intervene?

What Does an Investigating Judge Do and When Do They Intervene?

When a person receives a criminal court summons or becomes aware that proceedings have been initiated against them, one of the first questions that arises is who is in charge of the process and what authority they have to make decisions that may directly affect their life. The figure that appears at this initial stage is, in most cases, the investigating judge.

Many people are familiar with the term but not with the functions, powers, and limits of this judicial authority, which are essential to understanding how the Spanish criminal justice system operates.

In this article, we explain in detail what an investigating judge is, their main functions, the decisions they may take during the investigation phase, when they intervene in different types of proceedings, and the role they play in safeguarding the rights of individuals under investigation.

Who Is the Investigating Judge?

The investigating judge is the judge in charge of a Court of Investigation (Juzgado de Instrucción), one of the judicial bodies within the Spanish criminal system. Their primary function is to lead the investigation phase (fase de instrucción), the initial stage of criminal proceedings in which alleged criminal acts are examined, evidence is gathered, and it is determined whether there are sufficient grounds to proceed to trial or whether the case should be dismissed.

Unlike the judge who conducts the trial and delivers the judgment—typically a Criminal Court or Provincial Court depending on the seriousness of the offence—the investigating judge does not try or convict. Their role is to direct the investigation: acting as an impartial authority who supervises the actions of all parties, ensures legality, and adopts the necessary measures to clarify the facts without infringing fundamental rights.

This separation between the investigating judge and the trial judge is a key safeguard in the Spanish criminal system, ensuring impartiality in the final decision-making process.

When Does the Investigating Judge Intervene?

The investigating judge does not always intervene in the same way or at the same moment. Their involvement depends on how the proceedings are initiated and the specific circumstances of the case. Generally, their intervention arises in one of the following scenarios:

Following a Complaint or Criminal Claim

The most common scenario occurs when a complaint is filed by an individual, company, police authority, or public prosecutor, or when a formal criminal claim (querella) is lodged. The judge assesses whether the facts appear to constitute a criminal offence.

If sufficient indications exist, the judge issues an order opening preliminary proceedings and begins the investigation. If not, the case may be dismissed at the outset.

Upon Initiative of Police or Prosecution Authorities

The investigating judge may also act without a private complaint. This occurs when the judicial police detect potential criminal activity and submit a police report, or when the public prosecutor requests the opening of an investigation.

In Cases of Police Detention

When a person is detained, the investigating judge intervenes promptly to ensure the legality of the detention. Spanish law requires that detainees be brought before a judge within a maximum of 72 hours. The judge then decides whether to release the individual, order pre-trial detention, or impose alternative precautionary measures.

What Are the Functions of the Investigating Judge?

The investigating judge performs both an investigative role and a guarantee role, balancing fact-finding with the protection of fundamental rights.

Directing and Supervising the Investigation

The judge leads the investigation, determining which procedural steps are necessary and ensuring that police and prosecutorial actions comply with the law.

These steps may include taking statements from suspects and witnesses, ordering expert reports, conducting inspections, and reviewing financial or documentary evidence.

Authorising Searches and Intrusive Measures

The judge authorises investigative measures that affect fundamental rights, such as home searches or the interception of communications. Such measures require a reasoned judicial order demonstrating necessity and proportionality.

Taking the Suspect’s Statement

One of the most important procedural acts is the suspect’s statement before the judge. This takes place in court with full procedural safeguards and legal representation.

The suspect may remain silent, answer only certain questions, or testify freely—none of these choices may be used against them. Proper legal preparation is essential, as the statement can significantly influence the case.

Adopting Precautionary Measures

The judge may impose measures to ensure the proper conduct of proceedings, such as:

• Pre-trial detention
• Periodic court appearances
• Passport surrender
• Travel restrictions
• Restraining orders
• Financial bail

All such measures must comply with the principle of proportionality.

Deciding Whether the Case Proceeds or Is Dismissed

At the end of the investigation, the judge determines whether there is sufficient evidence to proceed.

• If not, the case is dismissed (either definitively or provisionally).
• If sufficient indications exist, the case is referred for trial.

What Can the Investigating Judge Not Do?

Understanding the limits of the investigating judge is as important as knowing their powers.

• They cannot issue a final judgment (except in minor offence cases).
• They cannot convict or acquit.
• They must respect fundamental rights and cannot impose measures without legal justification.

Their decisions are subject to appeal. The defence may challenge rulings before the same judge or before a higher court, such as the Provincial Court. This system of appeals ensures judicial oversight and protects against errors or abuses.

Why Is Legal Representation Crucial During the Investigation Phase?

The investigation phase lays the foundation of the entire case. The evidence gathered, statements given, and procedural steps taken at this stage largely determine the outcome of any subsequent trial.

A specialised criminal defence lawyer acts as a necessary counterbalance to the authority of the investigating judge and the prosecution. Their role includes:

• Ensuring procedural safeguards are respected
• Requesting favourable evidence
• Challenging unlawful evidence
• Preparing the client for statements
• Building a coherent defence strategy from the outset

Waiting until trial to seek legal representation is a serious mistake. Effective defence begins during the investigation phase.

Frequently Asked Questions

Can the investigating judge order my arrest at any time?

The judge may issue an arrest warrant where there are reasonable indications of criminal activity and specific risks (such as flight risk or destruction of evidence). This decision must always be justified and comply with legal requirements.

Can I access the case file while under investigation?

In general, yes. However, the judge may declare the proceedings confidential (secrecy of the investigation) for a limited period if disclosure could hinder the investigation.

What if the investigating judge makes a mistake or violates my rights?

Judicial decisions may be appealed. Your lawyer may file appropriate appeals before the same judge or higher courts. In cases of serious violations, a constitutional appeal may also be possible.

How long does the investigation phase last?

The duration varies depending on the complexity of the case. The law provides indicative timeframes (generally six months, extendable in complex cases), but in practice investigations may last longer. Your lawyer may request procedural acceleration if delays are excessive.