Difference Between Detention, Summons & Criminal Investigation

Difference between detention, summons, and criminal investigation

The language of criminal law is precise and technical, but in everyday use —in conversations, in the media, even in the accounts of those who have personally had contact with the justice system— its terms are mixed and confused with a frequency that can have very real consequences. Being detained, being summoned, and being investigated are three radically different situations in terms of their legal nature, their practical implications, and the rights that correspond to the person experiencing them. However, many people treat them as if they were equivalent or different degrees of the same situation.

This confusion is not harmless. Someone who believes they have been “investigated” when in reality they have been “detained” may not understand the urgency of the situation or act with the speed it requires. Someone who interprets a summons as if it were a detention may go to court in a state of unnecessary alarm that leads them to act counterproductively. And someone who does not understand what a criminal investigation consists of may fail to exercise their rights at the moment when it matters most.

In this article we explain clearly and in detail what each of these three figures is, how they differ, what obligations and rights each one generates, and what someone should do when they find themselves in any of these situations. A clear understanding of these differences is the first step to acting correctly when the criminal process knocks on your door, in whatever form it may take.

Detention: deprivation of liberty by the police

Detention is the most drastic and most immediate of the three figures. It consists of the deprivation of liberty of a person by the law enforcement agencies —National Police, Civil Guard, or regional police— when the legal requirements that justify it are present. Detention immediately suppresses the person’s freedom of movement: the detainee cannot move freely, cannot leave the place of custody, and is under the direct authority of the officers.

The conditions that may justify detention are, mainly, flagrante delicto —when the person is caught at the moment of committing the crime or immediately afterward— and the existence of reasonable indications of criminality sufficient to believe that the person has participated in the commission of a crime. Detention may also occur when there is an arrest warrant issued by a judge requiring the presence of the person under investigation.

Police detention is subject to a maximum time limit of 72 hours, after which the detainee must be released or brought before a judge. During that time, the detainee has a set of rights that must be respected from the very first moment: the right to know the reasons for the detention, the right to remain silent, the right not to testify against oneself, the right to legal assistance from a lawyer of their choice, and the right to have their detention communicated to a family member or trusted person.

Detention is, of the three figures, the one that requires the most urgent and immediate response. Every minute counts. The first thing to do when detained is to request the presence of a lawyer and not to make any statement until they arrive. There is no advantage in spontaneously “clarifying” things: everything said to the police can be used in the subsequent process, and doing so without legal advice is one of the most frequent and most harmful mistakes detainees make.

The summons: the court’s call to appear

A judicial summons is a completely different situation from detention. It does not involve any deprivation of liberty or the presence of police officers. It is simply the formal communication by which a judicial body requires a person to appear on a specific date, time, and place in order to participate in some procedural act within the criminal process.

The summons usually arrives by registered mail or through formal notification at the address of the person concerned. Its content includes the essential details of the act for which the person is called —court, date, time, case reference— and a warning of the consequences of failing to appear.

Unlike detention, which is a police action that occurs immediately, a summons is a judicial action that allows time for preparation. Between receiving the summons and the date of appearance there is a period —sometimes days, sometimes weeks— that should be used to consult a lawyer, understand the context of the proceedings, and properly prepare for the appearance.

The summons may require appearance in very different capacities, and that capacity determines the rights and obligations of the person appearing. It is not the same to be summoned as a suspect —in which case there is the right to remain silent and to legal assistance— as to be summoned as a witness —which implies the obligation to appear and to testify truthfully— or as a victim or injured party, which has its own procedural particularities.

The most important consequence of failing to appear at a judicial summons without justified cause is the imposition of a financial penalty and, in cases of repeated or persistent non-appearance, the possibility that the judge may order compulsory appearance before the court. In the most serious cases, this could lead to a warrant for search and arrest if the summoned person cannot be located.

Criminal investigation: when the court has opened proceedings

Criminal investigation —or, more technically, the investigation phase— is the process that the court initiates to clarify allegedly criminal acts. Unlike detention and summons, which are specific actions, the investigation is a procedure that unfolds over time, over weeks, months, or even years, and may include multiple procedural steps, appearances, and judicial decisions.

The person who is subject to a criminal investigation acquires the status of suspect (investigado), a term that since the reform of Organic Law 13/2015 replaced the former term “imputado.” Being investigated means that the court has considered that there are reasonable indications that the person may have participated in the acts under investigation. But —and this is fundamental— it does not mean being guilty of anything. The presumption of innocence continues to protect the suspect at all times.

The investigation may begin in various ways: from a complaint filed by the victim or a third party, from a police report, at the request of the public prosecutor, or on the initiative of the investigating judge. Once opened, the judge directs all actions aimed at clarifying the facts: taking statements, requesting expert reports, authorizing searches, analyzing documents, and carrying out any measure deemed necessary.

The criminal investigation concludes with one of two decisions: dismissal, if the judge does not find sufficient indications to continue, or an order to open trial proceedings if there is sufficient basis to bring charges and hold a trial. Between these two possibilities there is a period of uncertainty that may last a considerable time and that requires continuous legal assistance to ensure an effective defense throughout the investigation phase.

Key differences: a practical comparison

Who acts and under what authority
Detention is a police action, although in some cases it may be ordered by a judge through an arrest warrant. A summons is a court action, issued by the investigating judge or court clerk. The investigation is a procedure directed by the investigating judge, although the police and prosecution actively collaborate. This difference has important implications: detention can occur at any time and place; summons and investigation take place within a formal judicial process.

Impact on liberty
Detention involves the effective and immediate deprivation of liberty. A summons does not deprive liberty: the summoned person remains free until the appearance and does not lose liberty during it unless the judge orders precautionary measures. An investigation does not in itself deprive liberty, although it may involve measures that limit it —such as travel restrictions or periodic court appearances— and, in serious cases, may lead to pre-trial detention.

Time limits and duration
Police detention has a maximum limit of 72 hours, non-extendable except in exceptional terrorism cases. A summons sets a specific appearance date, but the prior period may vary. An investigation may last from weeks to several years, depending on complexity. The law establishes indicative time limits —six months for ordinary cases, twelve for complex ones— but in practice they may be much longer.

Rights in each situation
The detainee has the right to be informed of the reasons for detention, to remain silent, not to testify against themselves, to immediate legal assistance, to notify a family member, and to medical assistance if needed. A person summoned as a suspect has the right to know the charges, to remain silent, to legal assistance, and not to testify if they choose. A suspect during investigation has the right to access the case file, propose investigative measures, know the evidence against them, and be represented by a lawyer at all times.

Obligations in each situation
The detainee is not obliged to testify but must submit to identification procedures and lawful actions during detention. The summoned person must appear on the specified date, although if summoned as a suspect they are not obliged to testify. A witness, however, must both appear and testify truthfully, except in legally established exceptions. A suspect in investigation must appear when summoned by the judge but may exercise the right to silence.

The connections between the three figures: how the situation can evolve

These three figures are not isolated compartments: they often follow or interconnect within the same case. Understanding how a person’s situation may evolve is essential.

A person may be investigated and summoned to testify without ever being detained: this is common in economic crimes or fraud cases.
A person may be detained first and later summoned as a suspect after release: consistency between statements is crucial.
A person may be summoned as a witness and become a suspect based on their testimony: this is why legal advice is advisable even for witnesses.

What to do in each situation

If you are detained
Immediately request your lawyer. Do not make any statement, explanation, or clarification until you have spoken privately with them. Do not sign anything without legal review. Remember that remaining silent does not harm you.

If you receive a summons
Do not ignore it. Read it carefully and consult a criminal lawyer before attending court. Proper preparation is essential.

If you know you are under investigation
Act quickly. Hiring a specialized lawyer early is crucial to build a solid defense strategy from the outset.

Frequently asked questions

Can a summons turn into detention if I go to court?
Yes, although it is not common. If after hearing your statement the judge considers pre-trial detention justified, it may be ordered immediately, but legal requirements must be met.

Does being investigated prevent me from working or traveling?
No, unless the judge imposes specific precautionary measures.

Do I need a lawyer if summoned only as a witness?
Not mandatory, but highly advisable if there is any risk of implication.

Can the police investigate me without my knowledge?
Yes. Investigations may initially be confidential, and judicial secrecy may apply.

What is the difference between being summoned and receiving an arrest warrant?
A summons requires voluntary appearance; an arrest warrant orders police to deprive you of liberty and bring you before a judge.