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Investigations

What is an investigating judge, and do all civil-law systems have one?

Two incompatible offices share this English name. In France and Belgium a judge conducts an investigation. In Germany a judge acts on the prosecution’s application and checks whether the requested act is lawful. Both are officially called investigating judges.

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In short

An investigating judge is a member of the judiciary with a role in the investigation of a criminal case, before any trial. That is as far as a single definition can safely go, because the English phrase is used for two offices whose relationship to the investigation is opposite.

The directing type
A judge who conducts a judicial investigation: seised of a case, directing the gathering of evidence both for and against the suspect, and authorising the most intrusive measures. Belgium’s juge d’instruction / onderzoeksrechter and Portugal’s judge in the instrução phase work this way, and France may refer a case to an investigating judge.
The authorising type
A judge who does not own the investigation at all. The prosecution applies; the judge decides whether the requested act is legally permissible and performs the judicial acts. Germany’s Ermittlungsrichter under section 162 of the Strafprozessordnung is this kind of office.

Why it exists

The directing type exists because of a judgement that the most intrusive stage of a criminal process should be conducted by someone with judicial independence rather than by a party to it. The judge is charged with gathering evidence in both directions, which is a different posture from an investigator building a case.

AnalysisThe authorising type exists for a narrower reason: that an intrusive act should be checked by someone outside the investigating institution before it is done. That is a gate, not a leadership role, and it is compatible with the investigation belonging entirely to the prosecution.

How it works

Germany is the case that settles the terminology, because its own law uses the term for the second kind of office. Section 162 of the Strafprozessordnung is headed "Ermittlungsrichter", which the Federal Ministry of Justice’s official English translation renders as "Investigating judge".

What that judge does is set out in the same section. Under section 162(1), where the Staatsanwaltschaft considers a judicial investigative act necessary, it "stellt sie ihre Anträge" — submits its applications — to the local court. Under section 162(2), "Das Gericht hat zu prüfen, ob die beantragte Handlung nach den Umständen des Falles gesetzlich zulässig ist": the court must examine whether the requested act is legally permissible in the circumstances of the case. The judge is asked a question by the prosecution and answers it. The investigation itself belongs to the prosecution under section 160.

Belgium — two tracks
Criminal investigation is directed by the magistracy rather than the police. In the ordinary investigation the public prosecutor directs the enquiry; where more intrusive coercive measures are needed, an investigating judge is appointed to conduct a judicial investigation. The police carry out the investigative acts under that direction.
Portugal — an optional phase
A two-phase, magistrate-directed model. The prosecution directs the inquérito, and an investigating judge conducts the optional judicial-investigation phase, the instrução. The second phase is not automatic.
France — a referral
The procureur directs the investigation and decides what happens next, and one of the available paths is referring the matter to an investigating judge. The office is a destination for particular cases, not the default route for all of them.
Spain — alongside the prosecution
Spanish criminal procedure places the investigation under judicial and prosecutorial direction together: an investigating judge and the Ministerio Fiscal oversee the inquiry, and the police act as judicial police under that direction.
Italy — a different office again
The prosecutor directs the judicial police, and a separate figure — the giudice per le indagini preliminari, the judge for preliminary investigations — provides judicial oversight of the pre-trial phase, authorising intrusive measures and guarding the rights of the person under investigation. This is oversight and authorisation, not direction of the inquiry.

The office is also not permanent. Argentina’s federal jurisdiction moved to an accusatory process under the Federal Code of Criminal Procedure, in which the prosecution directs the investigation and the police act as its auxiliaries — replacing the older model in which an investigating judge led. Where the office exists, it exists because a legislature has kept it.

Common misconceptions

Widely held beliefs that do not match how the system actually operates.

  • Common belief: Every civil-law country has an investigating judge who leads investigations.

    In practice: Germany does not. Sections 160 and 163 of the Strafprozessordnung allocate the investigation between the prosecution and the police, and the judge under section 162 acts on application. Argentina’s federal system replaced its investigating-judge model. Italy has a judge for preliminary investigations who authorises and supervises rather than directs.

  • Common belief: An investigating judge is a trial judge who investigates.

    In practice: They are distinct offices with distinct functions. The point of a judicial investigation is that it produces a record for a court; a judge who conducted the investigation is not the judge who tries the case.

  • Common belief: If a country calls someone an investigating judge, that person runs the investigation.

    In practice: Germany’s official English translation applies the term to a judge who rules on applications made by the prosecution. The label does not tell you which of the two offices you are looking at.

  • Common belief: Judicial supervision makes an investigation fairer.

    In practice: No source here establishes that, and this site does not claim it. What judicial involvement changes is who is answerable and at what point; whether outcomes differ is an empirical question outside the scope of these sources.

How this varies between jurisdictions

A required section on every guide. Arrangements differ between countries, and we say how.

The useful question about any judge in an investigation is not what they are called but which of three things they do.

  1. Conduct the investigation — Belgium in the judicial-investigation track, Portugal in the instrução, France where a case is referred.
  2. Authorise particular acts on application — Germany under section 162, Italy through the judge for preliminary investigations.
  3. Neither, with authorisation held elsewhere in the judiciary — the common-law systems on this site, where warrants are issued by courts that have no other role in the inquiry.

The Netherlands has a rechter-commissaris, recorded in this corpus as existing with its powers not researched from the primary statutes. It is listed here as an instance of the office; which of the three roles above it performs is not established and is not asserted.

Rights and accountability

AnalysisBoth types perform the same underlying safeguard, at different points. Someone outside the investigating team has to approve the intrusive steps. Whether that person also directs the inquiry is a second question, and systems that answer it differently are not thereby providing more or less protection — they are locating it differently.

The German provision states the safeguard unusually plainly. The court’s task under section 162(2) is to examine whether the requested act is legally permissible in the circumstances of the case. Not whether it would be useful, and not whether the suspicion is strong enough to satisfy the investigator — whether the law permits it.

What we could not establish

  • The Dutch rechter-commissaris is recorded in the corpus as existing, and its powers were not researched from the primary statutes. It is named here as an instance of the office and nothing is claimed about what it may do.
  • The detailed powers of the Belgian and Portuguese investigating judges rest on official descriptions rather than on a full reading of the codes of criminal procedure.
  • This page describes what the office is and where it exists. It makes no claim that investigations supervised by a judge are fairer, more thorough or more reliable than those that are not.

Where to go next

Related: judicial police, who investigates crime, and what courts do.

Related topics

  • Who is legally responsible for investigating a crime?

    “The police” is an incomplete answer almost everywhere. Legal responsibility for an investigation may rest with police, with a prosecutor, or with a judge — and the body that performs the work is often not the body that owns it.

  • What does “judicial police” mean, and is it a police force?

    One term, at least three different things. In France it is a legal function exercised by designated personnel; in Brazil an institutional role held by named forces; in Italy personnel drawn from other forces who fall under judicial direction. It almost never means police employed by the judiciary.

  • How does a criminal investigation become a prosecution?

    The familiar picture is a relay: police investigate, then hand a file to a prosecutor who decides. That describes some systems. In others the prosecutor was legally responsible from the first day, and there is no handover to describe.

Where this connects

Institutions: Prosecution service, National police.

Sources

  1. Strafprozessordnung (StPO) § 162 — Ermittlungsrichter (German original text)

    Bundesministerium der Justiz / Bundesamt für Justiz (Gesetze im Internet) · Legislation · link verified 2026-08-25

    The authoritative German text of § 162 StPO, headed "Ermittlungsrichter", read directly. Supports § 162(1): where the Staatsanwaltschaft considers a judicial investigative act ("die Vornahme einer gerichtlichen Untersuchungshandlung") necessary, it SUBMITS ITS APPLICATIONS ("stellt sie ihre Anträge") to the Amtsgericht before public charges are preferred; and § 162(2): "Das Gericht hat zu prüfen, ob die beantragte Handlung nach den Umständen des Falles gesetzlich zulässig ist" — the court must examine whether the requested act is legally permissible in the circumstances of the case. Cited for the finding that the German Ermittlungsrichter acts ON APPLICATION and reviews LEGALITY, and does not direct or conduct the investigation, which § 160 places with the prosecution. It does not support any claim that Germany has a juge d'instruction-style judge who leads an investigation, and it establishes no investigative technique or threshold.

  2. Code of Criminal Procedure (Strafprozessordnung) — official English translation

    Bundesministerium der Justiz / Bundesamt für Justiz (Gesetze im Internet) · Legislation · link verified 2026-08-25

    The Federal Ministry of Justice's own English rendering of the StPO, read directly. Cited for ONE narrow and important fact: this official translation renders the heading of § 162 as "Investigating judge", and § 169 likewise refers to "investigating judges". That is the evidence that the English phrase "investigating judge" is applied, by an official source, to a German office whose function differs fundamentally from the French juge d'instruction — which is the terminology finding the investigating-judge page rests on. The German text is authoritative; this translation is cited as evidence of official English USAGE, not as a substitute for the German wording, which is quoted from the original.

  3. Strafprozessordnung (StPO) § 160 — Pflicht zur Sachverhaltsaufklärung (German original text)

    Bundesministerium der Justiz / Bundesamt für Justiz (Gesetze im Internet) · Legislation · link verified 2026-07-24

    Authoritative German text. Supports § 160(1): once the Staatsanwaltschaft learns of a suspected offence it must investigate the facts in order to decide whether to bring a public charge; and § 160(2): it must investigate exculpatory as well as incriminating circumstances and secure evidence. Supports the allocation of investigative responsibility and the objectivity duty. Does NOT support any description of investigative technique, thresholds, or practice.

  4. Article 12 du Code de procédure pénale

    République française (Légifrance) · Legislation · 1958-04-08 · link verified 2026-07-24

    Supports the exact wording that the police judiciaire is exercised 'sous la direction du procureur de la République' by the officers, officials and agents designated in that title. Légifrance records the provision as in force from 8 April 1958 and as scheduled for repeal by Ordonnance n° 2025-1091 of 19 November 2025 with effect from 1 January 2029; any citation must state that it is current law carrying a scheduled end date. Does NOT support any claim about which bodies those designated officers belong to, nor about investigative practice.

  5. Les magistrats du parquet

    Ministère de la justice (France) · Government publication · link verified 2026-07-24

    Supports: the definition of the parquet / ministère public; the 'magistrature debout' description and the siège/parquet distinction; the hierarchy from procureur général to procureur de la République; that parquet magistrates act 'sous l'autorité du ministre de la Justice' and receive 'des instructions générales du ministre de la Justice mais en aucun cas dans les dossiers judiciaires'; that they do not benefit from the guarantee of inamovibilité; and the prosecutor's direction of investigation and discretion over case outcomes. An official self-description of the formal rule. It does NOT establish that the rule is observed in practice, and cannot settle the contested question of prosecutorial independence in either direction.

  6. National justice systems — Belgium (European e-Justice Portal)

    European Commission (European e-Justice Portal) · International organisation · link verified 2026-07-26

    The European Commission's e-Justice portal page on Belgium, read directly. Supports the ordinary-court hierarchy — courts of first instance across 12 judicial districts, five courts of appeal ("Brussels, Liege, Mons, Ghent and Antwerp"), and the Court of Cassation (Cour de cassation / Hof van Cassatie) at the apex; the prosecution as the "State Counsel's Office or Prosecutor's Office (ministère public / openbaar ministerie)", the "standing judges" (magistrature debout / staande magistratuur, the parquet / parket) distinct from the "sitting judges" who adjudicate; and Article 151(1) on the independence of judges. An intergovernmental (EU) source describing Belgium.

  7. Code of Criminal Procedure (Código de Processo Penal), consolidated text

    Portugal — consolidated Código de Processo Penal (official-origin text) · Legislation · link verified 2026-07-26

    A consolidated Code of Criminal Procedure text, fetched as a PDF and text-extracted. Supports Art. 263(1) ("a direcção do inquérito cabe ao Ministério Público, assistido pelos órgãos de polícia criminal" — the Public Prosecution Service directs the investigation phase, assisted by the criminal-police bodies) and Art. 17 (the investigating judge, juiz de instrução, conducts the optional judicial-investigation phase, the instrução, and acts as guarantor of rights). Establishes the two-phase, magistrate-directed investigation model.

  8. Constitución Española de 1978

    Boletín Oficial del Estado (boe.es), BOE-A-1978-31229 · Legislation · 1978-12-29 · link verified 2026-07-26

    The authoritative Castilian text, read in full. Supports: art. 2 (the indissoluble unity of the Spanish Nation and the right to autonomy of the nationalities and regions); art. 137 (the State organised into municipalities, provinces and Autonomous Communities); art. 145.1 ('En ningún caso se admitirá la federación de Comunidades Autónomas' — federation is constitutionally forbidden, so Spain is a decentralised UNITARY state); art. 148 (competences the Communities MAY assume) and art. 149.1 (the State's EXCLUSIVE competences), including art. 149.1.6 ('Legislación mercantil, penal y penitenciaria; legislación procesal' — criminal, penitentiary and procedural LEGISLATION is exclusively the State's), art. 149.1.5 (Administration of Justice), and art. 149.1.29 (public security, 'sin perjuicio de la posibilidad de creación de policías por las Comunidades Autónomas' — the basis for autonomous police); art. 104 (security forces under the Government); art. 117.5 ('El principio de unidad jurisdiccional es la base de la organización y funcionamiento de los Tribunales' — judicial unity); art. 122 (the Consejo General del Poder Judicial as the judiciary's governing body); art. 123 (the Tribunal Supremo, 'con jurisdicción en toda España, es el órgano jurisdiccional superior en todos los órdenes'); art. 124 (the Ministerio Fiscal, national, acting under unidad de actuación y dependencia jerárquica); art. 152.1 (a Tribunal Superior de Justicia culminating the judicial organisation in each community, without prejudice to the Supreme Court); and arts. 24-25 (due-process and penal principles). WAVE 19 ADDITION, read from the same authoritative Castilian text. Supports art. 53.1, that the rights and liberties recognised in Chapter Two bind all public powers and may be regulated only by law respecting their essential content, protected in accordance with art. 161.1.a); and art. 53.2 in terms: "Cualquier ciudadano podrá recabar la tutela de las libertades y derechos reconocidos en el artículo 14 y la Sección primera del Capítulo segundo ante los Tribunales ordinarios por un procedimiento basado en los principios de preferencia y sumariedad y, en su caso, a través del recurso de amparo ante el Tribunal Constitucional" — protection is sought first before the ORDINARY courts by a preferential and summary procedure, and where appropriate thereafter by amparo before the Constitutional Court. Supports art. 54, that an organic law regulates the Defensor del Pueblo as high commissioner of the Cortes Generales for the defence of the rights in that Title, who may supervise the activity of the Administration and reports to the Cortes. Cited for the SEQUENCE — ordinary courts first, constitutional court where appropriate — and not for any claim about admissibility criteria or outcomes. WAVE 20 ADDITION. Read from the same authoritative Castilian text on the BOE. Spain writes the emergency architecture into the constitution itself in more detail than almost any system in this wave. Supports Constitución Española de 1978, Art. 116(1): “1. Una ley orgánica regulará los estados de alarma, de excepción y de sitio, y las competencias y limitaciones correspondientes.”. Supports Constitución Española de 1978, Art. 116(2), (3) and (4): “2. El estado de alarma será declarado por el Gobierno mediante decreto acordado en Consejo de Ministros por un plazo máximo de quince días, dando cuenta al Congreso de los Diputados, reunido inmediatamente al efecto y sin cuya autorización no podrá ser prorrogado dicho plazo. El decreto determinará el ámbito territorial a que se extienden los efectos de la declaración. 3. El estado de excepción será declarado por el Gobierno mediante decreto acordado en Consejo de Ministros, previa autorización del Congreso de los Diputados. La autorización y proclamación del estado de excepción deberá determinar expresamente los efectos del mismo, el ámbito territorial a que se extiende y su duración, que no podrá exceder de treinta días, prorrogables por otro plazo igual, con los mismos requisitos. 4. El estado de sitio será declarado por la mayoría absoluta del Congreso de los Diputados, a propuesta exclusiva del Gobierno. El Congreso determinará su ámbito territorial, duración y condiciones.”. Supports Constitución Española de 1978, Art. 55(1): “1. Los derechos reconocidos en los artículos 17, 18, apartados 2 y 3, artículos 19, 20, apartados 1, a) y d), y 5, artículos 21, 28, apartado 2, y artículo 37, apartado 2, podrán ser suspendidos cuando se acuerde la declaración del estado de excepción o de sitio en los términos previstos en la Constitución. Se exceptúa de lo establecido anteriormente el apartado 3 del artículo 17 para el supuesto de declaración de estado de excepción.”. Supports Constitución Española de 1978, Art. 116(5); cf. Ley Orgánica 4/1981 Art. 1.Cuatro ("La declaración de los estados de alarma, excepción y sitio no interrumpe el normal funcionamiento de los poderes constitucionales del Estado."): “5. No podrá procederse a la disolución del Congreso mientras estén declarados algunos de los estados comprendidos en el presente artículo, quedando automáticamente convocadas las Cámaras si no estuvieren en período de sesiones. Su funcionamiento, así como el de los demás poderes constitucionales del Estado, no podrán interrumpirse durante la vigencia de estos estados. Disuelto el Congreso o expirado su mandato, si se produjere alguna de las situaciones que dan lugar a cualquiera de dichos estados, las competencias del Congreso serán asumidas por su Diputación Permanente.”. Supports Constitución Española de 1978, Art. 117(5)-(6); Ley Orgánica 4/1981 Art. 35 ("En la declaración del estado de sitio el Congreso de los Diputados podrá determinar los delitos que durante su vigencia quedan sometidos a la Jurisdicción Militar."): “5. El principio de unidad jurisdiccional es la base de la organización y funcionamiento de los Tribunales. La ley regulará el ejercicio de la jurisdicción militar en el ámbito estrictamente castrense y en los supuestos de estado de sitio, de acuerdo con los principios de la Constitución. 6. Se prohíben los Tribunales de excepción.”. Cited for the three graded regimes, the closed list of suspendable rights and the express bar on suspension under the estado de alarma, the institutional-continuity guarantee, and the confinement of military jurisdiction. It records no declaration and supports no claim about any other country.WAVE 21 ADDITION. Read from the same BOE consolidated text, article by article. Supports Art. 17(1)-(4): “1. Toda persona tiene derecho a la libertad y a la seguridad. Nadie puede ser privado de su libertad, sino con la observancia de lo establecido en este artículo y en los casos y en la forma previstos en la ley. 2. La detención preventiva no podrá durar más del tiempo estrictamente necesario para la realización de las averiguaciones tendentes al esclarecimiento de los hechos, y, en todo caso, en el plazo máximo de setenta y dos horas, el detenido deberá ser puesto en libertad o a disposición de la autoridad judicial. 3. Toda persona detenida debe ser informada de forma inmediata, y de modo que le sea comprensible, de sus derechos y de las razones de su detención, no pudiendo ser obligada a declarar. Se garantiza la asistencia de abogado al detenido en las diligencias policiales y judiciales, en los términos que la ley establezca. 4. La ley regulará un procedimiento de «habeas corpus» [...]” Supports Art. 18(1)-(4): “1. Se garantiza el derecho al honor, a la intimidad personal y familiar y a la propia imagen. 2. El domicilio es inviolable. Ninguna entrada o registro podrá hacerse en él sin consentimiento del titular o resolución judicial, salvo en caso de flagrante delito. 3. Se garantiza el secreto de las comunicaciones y, en especial, de las postales, telegráficas y telefónicas, salvo resolución judicial. 4. La ley limitará el uso de la informática para garantizar el honor y la intimidad personal y familiar de los ciudadanos y el pleno ejercicio de sus derechos.” Supports Art. 19, and specifically its rights-holder wording: “Los españoles tienen derecho a elegir libremente su residencia y a circular por el territorio nacional” — against Art. 17(1)'s “Toda persona”. Supports Art. 24(1)-(2), including the right to effective judicial protection without indefensión, and the rights “al Juez ordinario predeterminado por la ley, a la defensa y a la asistencia de letrado, a ser informados de la acusación formulada contra ellos, a un proceso público sin dilaciones indebidas y con todas las garantías, a utilizar los medios de prueba pertinentes para su defensa, a no declarar contra sí mismos, a no confesarse culpables y a la presunción de inocencia”. Supports Art. 24(1) verbatim, including the phrase quoted on the equality-of-arms page: “1. Todas las personas tienen derecho a obtener la tutela efectiva de los jueces y tribunales en el ejercicio de sus derechos e intereses legítimos, sin que, en ningún caso, pueda producirse indefensión.” Supports Art. 53(1) AND 53(2): “1. Los derechos y libertades reconocidos en el Capítulo segundo del presente Título vinculan a todos los poderes públicos. Sólo por ley, que en todo caso deberá respetar su contenido esencial, podrá regularse el ejercicio de tales derechos y libertades, que se tutelarán de acuerdo con lo previsto en el artículo 161, 1, a). 2. Cualquier ciudadano podrá recabar la tutela de las libertades y derechos reconocidos en el artículo 14 y la Sección primera del Capítulo segundo ante los Tribunales ordinarios por un procedimiento basado en los principios de preferencia y sumariedad y, en su caso, a través del recurso de amparo ante el Tribunal Constitucional.” Constitutional text only — no decision of the Tribunal Constitucional, no provision of the Ley de Enjuiciamiento Criminal, nothing about any other country.

  9. Constitution of the Italian Republic (1948) — official English translation

    Corte costituzionale (Constitutional Court of the Italian Republic) · Legislation · 1948 · link verified 2026-07-26

    The Constitutional Court's own official English translation (October 2023 edition), fetched as a PDF and text-extracted (confirmed by the research and verification passes; the Senate's English PDF was bot-walled, so this Court edition was substituted). Supports Art. 101 (justice administered in the name of the people; the judiciary subject only to the law), Art. 104 (the judiciary an independent branch; the High Council of the Judiciary/CSM), Art. 107 (the public prosecutor's guarantees), Art. 109 ("judicial authorities may directly avail themselves of the judicial police"), Art. 112 ("the public prosecutor shall have the obligation to initiate criminal proceedings" — mandatory prosecution), Art. 103 (the Council of State and administrative justice), Art. 116 (the five special-autonomy regions, with additional devolution over "justice" limited to the organizational requirements of the Justice of the Peace), Art. 117(2) — subparagraphs (l) "jurisdiction and procedural law; civil and criminal law; administrative justice", (h) "public order and security, save for local administrative police", (d) defence — establishing that all four justice functions are EXCLUSIVE State competence, and Arts. 134–135 (the Constitutional Court).

  10. Federal Code of Criminal Procedure (CPPF) — accusatory system (Law 27.482)

    Ministerio Público Fiscal / InfoLEG (Argentina) · Legislation · 2019-01-07 · link verified 2026-07-27

    The Federal Code of Criminal Procedure (originally Law 27.063, reformed and renamed by Law 27.482, published in the Official Gazette on 7 January 2019), confirmed in two independent passes via the Public Prosecution Service and InfoLEG. Supports that the federal criminal process moved from an inquisitorial to an accusatory/adversarial system in which the Public Prosecution Service (Ministerio Público Fiscal) directs the criminal investigation, with the police acting as auxiliaries; and that the system is being implemented in phases across the federal jurisdictions.

  11. Types of legal professions — Netherlands (European e-Justice Portal)

    European Commission (European e-Justice Portal) · International organisation · link verified 2026-07-26

    The European Commission's e-Justice portal page on the Netherlands, read directly. Supports: "The public prosecutor is in charge of investigations"; that at national level the OM is governed by the Board of Prosecutors General in The Hague; and that "political responsibility for the OM lies with the Minister for Justice", who together with the Board decides priorities for investigation and prosecution. An intergovernmental (EU) source describing the Netherlands; it establishes the prosecutor-led investigation and the OM's subordination to ministerial political responsibility.