Why entrust the internal investigation to a lawyer: legal professional privilege, ethical rules and access to the court for investigations?

Updated 9 November 2026

Key contacts: Pascal-André Gérinier (Lawyer - Founder), William Mak (Lawyer - Founder)

Three reasons. Legal professional privilege (secret professionnel): where the lawyer investigates as the company's counsel, the interview notes and the report delivered to the company are covered by Article 66-5 of the Act of 31 December 1971, the company remaining free to produce the report in court. Ethical rules: the rules of the profession govern the interviews; the lawyer tells the persons interviewed that they are not their lawyer, informs those against whom facts could be alleged that they may be assisted, and does not subsequently represent the company against a person they have interviewed. The court: where the evidence is held by a third party or risks disappearing, only the court can order an ex parte evidentiary report (Article 145 of the French Code of Civil Procedure) or a prohibition under a periodic penalty payment in interim proceedings (référé), and authorise a protective attachment; the lawyer prepares and presents these applications, which no HR consultancy or private investigator can do for you.

Key points

• Privilege covers what the lawyer delivers to their client when investigating as their counsel, not the persons they interview: they are so informed. The work of a lawyer appointed as an independent investigator is not covered by this privilege.
• Five judicial measures extend the investigation, which the court orders or authorises and the lawyer prepares: ex parte evidentiary report, interim proceedings, protective attachment, infringement seizure, compulsory production of documents; to these are added the criminal route and two contractual instruments reserved for parties assisted by a lawyer: the participatory procedure and the lawyer-countersigned deed.
• Before the judicial court, representation by a lawyer is in principle compulsory for these applications; the company may, on the other hand, lodge a complaint on its own.
• The lawyer who conducted the investigation does not subsequently represent the company against a person they interviewed: another lawyer takes over.
• Abroad, confidentiality varies: strong in Hong Kong, weak in China.

When you entrust an internal investigation to a lawyer, three things change. The engagement falls within an ethical framework. Entrusted to a 360° law firm such as MOSAIK, it also benefits from all the skills that a sensitive situation calls into play, employment law, business criminal law, company law, compliance, personal data and international matters, without the company having to multiply its advisers. The work delivered to the client benefits from legal professional privilege under the conditions of Article 66-5 of the Act of 31 December 1971. The firm can handle the ensuing litigation through a lawyer other than the investigator: the ethical rules require the latter to refrain from representing the company against a person interviewed, and the involvement of a colleague from the same firm is assessed in the light of the rules on conflicts of interest. The court assesses the probative value of any internal investigation in the light of the other evidence in the file (Cass. soc. 18 juin 2025, n° 23-19.022): it is the lawyer's method, fair and documented, that gives the report its weight.

What legal professional privilege covers, and what it does not

Article 66-5 covers, in all matters, the advice given by the lawyer to their client, the correspondence exchanged between them, interview notes and, more generally, all the documents in the file. Applied to the internal investigation, everything depends on the engagement. Where the lawyer investigates as the company's counsel, the assistance engagement, the engagement letter, the notes taken during the interviews, the exchanges with management and the report delivered to the body that mandated them are covered. Where the lawyer is appointed as an independent investigator, the expert engagement, the investigation is not subject to the lawyer's legal professional privilege, and the lawyer keeps these documents separate from their other files. In both cases, the privilege, where it exists, is that of the relationship between the lawyer and their client: it does not protect the persons interviewed, who are so informed, and it does not prevent the company from producing the report before the court if it so decides; once produced, the report is debated like any other document. It is distinct from the confidentiality of in-house lawyers' legal opinions, established by Act No. 2026-122 of 23 February 2026, which creates an Article 58-1 in the Act of 31 December 1971: narrower, subject to its own conditions, and whose entry into force is deferred to a decree.

In practice, the report is delivered to the body of the company that mandated the lawyer. Its circulation must remain limited to those who need to know. If the company chooses to produce it in court, it favours fair and complete disclosure, or precisely justifies the necessary omissions: an investigation whose interview records were only partly produced was held to be insufficiently probative (Cass. soc. 18 juin 2025). Before each interview, the lawyer makes clear to the persons interviewed that they are not the lawyer's clients, that legal professional privilege does not protect them and that what they say may be used. The lawyer informs them of the possibility of being assisted. Finally, the report distinguishes the facts found, the statements collected and the legal analysis.

Two engagements are defined from the engagement letter onwards, because they do not follow the same rules. The first establishes the facts: interviews, timeline, documentary analysis, findings and report, within a scope and with rights for the persons concerned set at the outset. The second confidentially advises the company on the follow-up: protective measures, disciplinary procedure, updating of the internal rules and procedures, legal obligations, litigation and remediation. Distinguishing them avoids confusing a factual finding with a legal opinion, and allows the company to produce the former in court while keeping the latter to itself.

The ethical rules of the investigating lawyer: what they impose on themselves

The profession's ethical rules distinguish two engagements: assistance, where the lawyer investigates as the company's counsel, and expert appointment, where they investigate independently. In both cases, the lawyer undertakes to:

• tell each person interviewed that they are not their lawyer and that they are acting on behalf of the client who instructed them;
• make clear to them that the legal professional privilege owed to the client does not extend to them: what they say may be used by the company;
• inform them, where facts could be alleged against them, that they may be assisted by a lawyer;
• explain their engagement and its non-coercive nature, conduct the exchanges fairly and refrain from any pressure;
• transcribe statements faithfully and, where they are recorded verbatim, offer the reading over and signature of the written record;
• in an assistance engagement, refrain from subsequently representing their client in proceedings brought against a person they have interviewed; in an expert engagement, refrain from representing any party in any proceedings, even amicable, connected with the investigation.

The Conseil national des barreaux published in June 2020 a guide on lawyers and internal investigations, which supplements these reference points. These rules guide the method without prejudging the conclusions of the investigation, and they explain why the lawyer who investigates is not the one who subsequently pleads, the involvement of another lawyer from the firm remaining subject to the rules on conflicts of interest.

Judicial measures in support of the investigation

The internal investigation stops at the company's door: it binds neither a former employee, nor a competitor, nor a service provider, nor a bank. Where the evidence is in their hands, or risks disappearing, the next step is judicial, and that is where the strength of a 360° firm comes fully into play: the same firm that conducted the investigation prepares the judicial measures. Three levels must be distinguished. What only the court can do: order an evidentiary report, a prohibition, an attachment, the production of documents. What only a lawyer can do: represent the company before the judicial court (tribunal judiciaire), where representation is in principle compulsory, assist the parties in a participatory procedure agreement, which only parties assisted by a lawyer may conclude, countersign a lawyer-countersigned deed, and plead thereafter. What the lawyer prepares without having exclusivity over it: the criminal complaint, which the company may lodge on its own, but whose form, simple complaint or complaint with a civil party application, determines its effects. There follow five judicial measures, the criminal route and two contractual instruments, with, for each, the typical situation, the condition and the limit.

1. The ex parte evidentiary report under Article 145 of the French Code of Civil Procedure

If there is a legitimate reason to preserve or establish, before any trial, evidence of facts on which the outcome of a dispute may depend, the court may order any legally admissible investigative measure, on an ex parte application or in interim proceedings (Article 145). On an ex parte application, that is, without the opposing party being forewarned, which the applicant must justify (Article 493), a court bailiff (commissaire de justice), often accompanied by an IT expert, attends the premises of the competitor that hired the employee who left with the customer list, of the service provider or at the former employee's business address, copies mailboxes and drives on the basis of defined keywords and a defined period, and places everything under sequestration; the sorting then takes place with both parties present, and the opposing party may apply for the order to be withdrawn. Conditions: a legitimate reason, a legally admissible measure proportionate to the aim pursued, an application that justifies the element of surprise. On the employee's side, the same route makes it possible to obtain, before any trial, comparative data to prove discrimination (Cass. soc. 22 septembre 2021, n° 19-26.144), or the production of an investigation report.

2. Interim proceedings (référé)

Where a former employee is using files they took with them, the company may ask the president of the judicial court, in interim proceedings, for a prohibition under a periodic penalty payment or the handing over of documents: Article 835 of the French Code of Civil Procedure makes it possible to prevent imminent harm or put an end to a manifestly unlawful disturbance. In employment matters, the interim relief formation of the labour court (conseil de prud'hommes) has comparable powers (Article R. 1455-6 of the French Labour Code). Conversely, where the employer fails to act after an alert from an elected works council (CSE) member, the employee or the elected member may apply to the labour court under the expedited procedure on the merits (Article L. 2312-59). Interim proceedings remain adversarial: they do not allow the element of surprise and do not decide the merits.

3. Protective attachment

Where misappropriation is plausible, the lawyer asks the court for authorisation to attach, as a protective measure, the accounts or assets of the presumed perpetrator, before any judgment, provided the claim appears well founded in principle and circumstances threaten its recovery (Article L. 511-1 of the French Code of Civil Enforcement Procedures). The attachment makes the sums unavailable without transferring them; on pain of lapse, it must be followed, within the period set by the legislation, by an action on the merits to obtain an enforceable title.

4. Infringement seizure (saisie-contrefaçon)

Files, software, databases or creative works have been taken and infringement is suspected. The infringement seizure makes it possible, on an order made on an ex parte application by the president of the judicial court with jurisdiction in intellectual property, to have the allegedly infringing items described or seized by a court bailiff. It helps to preserve evidence that is difficult to obtain otherwise, without prejudging the existence of the rights relied on or their infringement. Its scope depends on the intellectual property rights actually protected. An action on the merits must then be brought within the statutory period, failing which the seizure is void, on the application of the party against whom it was carried out. The Intellectual property page details these actions.

5. Compulsory production of documents during proceedings

Once proceedings are under way, a party may ask the court to order a third party to produce a document in its possession, if need be under a periodic penalty payment (Articles 138 et seq. of the French Code of Civil Procedure). Before the labour court as before the judicial court, this is how one obtains a register, a badge record, a contract or an email whose existence is known but of which one holds no copy.

6. The criminal route

Faced with a suspected offence, the company may lodge a simple complaint with the public prosecutor or a complaint with a civil party application; the latter requires in principle a refusal to prosecute or a period of three months after the prior complaint, and a company attaches its balance sheet and profit and loss account (Article 85 of the French Code of Criminal Procedure). The criminal investigation allows searches, bank and telephone requisitions and interviews, beyond the employer's powers. The two-month disciplinary period is interrupted only by setting the public prosecution in motion: a preliminary police investigation is not sufficient (Article L. 1332-4 of the French Labour Code; Cass. soc. 13 octobre 2016, n° 15-14.006), nor, consequently, is a simple complaint: the form chosen matters. The March 2023 guide of the French Anti-Corruption Agency and the National Financial Prosecutor's Office recommends an autonomous and fair internal investigation and the preservation of evidence for the investigators. The lawyer liaises with the public prosecutor. A knowingly false complaint exposes its author to prosecution.

7. The participatory procedure agreement

Where the implicated person, or a partner, agrees to cooperate, the parties, assisted by their lawyers, may conclude a participatory procedure agreement to resolve their dispute amicably or prepare their case for trial (Articles 2062 and 2064 of the French Civil Code): appointment of a technical expert, interviews organised by mutual agreement, timetable for the exchange of documents. Only a party assisted by a lawyer may conclude one. It avoids or shortens the trial, and what is established in it may be relied on before the court.

8. The lawyer-countersigned deed

An investigation may lead to a settlement, a confidentiality undertaking or an acknowledgement of debt after misappropriation. These agreements may take the form of a private deed countersigned by the parties' lawyers: under Article 1374 of the French Civil Code, such a deed is conclusive evidence of their handwriting and signature and dispenses with the handwritten statements required by law. The countersignature attests to the parties' handwriting and signature; it does not guarantee the validity of the clauses and does not, by itself, constitute an enforceable title, except for a settlement or an agreement resulting from a participatory procedure, mediation or conciliation, countersigned by the lawyers of each party and endorsed with the enforcement formula by the court registry (Article L. 111-3, 7°, of the French Code of Civil Enforcement Procedures).

A point on form. Before the judicial court, representation by a lawyer is in principle compulsory, including for an ex parte application or interim proceedings, save for exemptions, in particular for claims not exceeding 10,000 euros; before the labour court and the commercial court, it is not always compulsory. In all cases, the success of a measure depends on the drafting of the application, the choice of the competent court and how it fits with the investigation: an evidentiary report carried out after the implicated person has been interviewed risks finding nothing.

Lawyer, in-house lawyer, HR consultancy, private investigator: the table

The report in the face of a search

In an assistance engagement, the interview notes and the report delivered to the client are covered by legal professional privilege. A search of a law firm follows a special procedure: it is conducted by a judge, on a written and reasoned decision of the liberty and custody judge, in the presence of the bâtonnier (head of the local bar), who may object to the seizure of a document covered by privilege, with that same judge ruling on the objection (Article 56-1 of the French Code of Criminal Procedure). The protection is not absolute: it gives way if the lawyer is themselves suspected of having taken part in the offence; since 1 March 2022, advice privilege cannot be relied on against investigations into tax fraud, corruption, influence peddling, terrorist financing and the laundering of those offences where the documents establish that they were used to commit or facilitate the offence (Article 56-1-2); and it does not extend to documents that existed before the investigation and that the company holds in any event. The company searched may, for its part, object to the seizure of a document covered by privilege found on its premises (Article 56-1-1). The real point lies elsewhere: a report kept at the lawyer's office and delivered only to the mandating body, rather than circulated within the company, remains under control.

Abroad: variable confidentiality

In a cross-border investigation, the protection of communications varies from country to country. In Hong Kong, common law legal professional privilege comprises legal advice privilege and litigation privilege, whose conditions differ. In Mexico, professional secrecy is recognised, but its procedural protection is more limited. In China, the lawyer is bound by confidentiality, but no comparable procedural protection covers communications, and cooperation with the authorities may be expected. The circulation of sensitive information must therefore be organised, it must be determined where legal analyses will be drawn up and kept, and the work must then be coordinated with local counsel. French protection does not transpose automatically abroad.

The guide How to conduct an internal investigation in an international group? details the rules country by country. For the method of the investigation itself, see How to conduct an internal investigation into harassment or discrimination?; to find out who pays, Who should pay for an internal investigation?; for the approach as a whole, the Internal investigations page. The actions that extend the investigation also fall under our Unfair competition and free riding and Intellectual property pages.