When can evidence from a European Investigation Order be challenged?

Short answer

Directive 2014/41/EU creates mutual recognition for European Investigation Orders (EIOs), not automatic legality or admissibility. Before issuing an EIO, the issuing authority must find it necessary and proportionate, respect defence rights, and confirm that the same measure could lawfully be ordered in a comparable domestic case. The executing authority generally recognises it, but may use a less intrusive alternative and may refuse on the Directive's limited grounds, including a concrete incompatibility with Charter rights.

Challenges are divided between states. The substantive reasons for issuing the order—why the evidence was sought, and whether the issuing-state conditions were met—normally must be challenged in the issuing state. Recognition, execution and the manner in which a search, hearing, interception or transfer was carried out can be challenged through remedies equivalent to those available for a similar domestic measure in the executing state.

The Directive does not harmonise trial admissibility or create a rule that every EIO defect automatically excludes evidence. National law normally decides admissibility, subject to equivalence, effectiveness and Charter Articles 47 and 48. Under M.N. (EncroChat), C-670/22, a criminal court must disregard information or evidence where the accused cannot effectively comment on material likely to influence the factual assessment. Other defects require the national court to provide a remedy that effectively protects the breached EU right; suppression is one possible remedy, not an automatic universal consequence.

The issuing state carries the first legality check

An EIO is a judicial decision issued or validated to have one or more investigative measures carried out in another participating Member State. It can also request evidence already held by the executing authorities. Denmark and Ireland do not participate in the Directive.

Article 6 permits issue only where:

1. the measure is necessary and proportionate for the proceedings, taking account of the suspected person's rights; and
2. the measure could have been ordered under the same conditions in a similar domestic case.

The EIO must be “necessary and proportionate” and respect the rights of the suspected or accused person. — Directive 2014/41/EU, Article 6

That requires more than filling in the standard form. The issuing authority should identify the offence, evidential purpose, person or premises, requested measure, relevant procedural status and why a narrower route is inadequate. Where domestic law requires a judge for the equivalent measure, routing it through a prosecutor cannot evade that safeguard.

In Staatsanwaltschaft Wien, C-584/19, the Court held that a public prosecutor may be an EIO issuing authority even if exposed to individual instructions from the executive. Unlike a European Arrest Warrant, an EIO does not itself impose detention, and execution remains subject to review in both states. That institutional rule does not remove Article 6's domestic-authorisation condition.

An EIO may also be issued at the request of the defence where national criminal procedure allows it. The Directive does not give the prosecution exclusive access to cross-border evidence.

What the executing authority checks

The executing authority must generally recognise the EIO without further formality and execute it as if the measure had been ordered domestically. It follows the issuing authority's requested formalities unless they conflict with the executing state's fundamental legal principles.

Mutual recognition still permits adjustment. Under Article 10, the executing authority should use another measure where the requested one does not exist, would not be available in a similar domestic case, or the alternative would achieve the same result with less interference. It should consult the issuing authority before substitution or non-execution.

Article 11's refusal grounds include, depending on the measure:

• immunity or privilege, and protected press or broadcasting freedom;
• harm to essential national-security interests or protected intelligence sources;
• ne bis in idem;
• conduct committed mainly in the executing state that is not an offence there;
• substantial grounds to believe execution would breach Treaty or Charter rights;
• lack of double criminality outside the Annex D offence categories and thresholds; and
• measure-specific restrictions where domestic law reserves the technique for certain offences.

The fundamental-rights ground is concrete, not a general licence to retry the issuing state's assessment. The executing authority should identify the individual risk, request information and consider safeguards. It must refuse where substantial grounds show that execution itself would breach a Charter right and the risk cannot be resolved.

Execution can also be postponed where it would prejudice an ongoing investigation or the relevant objects are already being used in other proceedings. Postponement is temporary and should be reviewed once the reason ends.

Illegality can arise in either state

Three legal layers should be separated:

• Issue: Was the EIO necessary, proportionate, issued or validated by the correct authority, and domestically available in the issuing state?
• Execution: Were search, seizure, interception, hearing, privilege and data-handling rules observed in the executing state, including requested formalities?
• Use: Can the resulting material fairly be admitted, tested and relied on in the issuing state's trial?

A defect at one layer does not answer every later question. For example, evidence may have been gathered lawfully by one state before the EIO, with the EIO merely transferring evidence already held. Conversely, a formally valid order may be executed by an unlawful search. The defence needs the order, validation, execution record, chain of custody and applicable national decisions to identify the right challenge.

The M.N. judgment concerned encrypted EncroChat data already available to French authorities and transferred to Germany. The Court held that an EIO for such evidence can be issued by a public prosecutor where that prosecutor could order the comparable domestic transfer. Whether the original interception satisfied the executing state's conditions was not automatically for the German issuing authority to reassess; mutual trust and the division of functions mattered.

Where and how to challenge

Article 14 requires legal remedies equivalent to those available against a similar domestic investigative measure. It then allocates the dispute:

“The substantive reasons for issuing the EIO may be challenged only” in the issuing state. — Directive 2014/41/EU, Article 14(2)

The executing state nevertheless remains responsible for remedies against its recognition and execution and for its fundamental-rights guarantees. Authorities must provide timely information about available remedies where investigation confidentiality permits, apply domestic-equivalent time limits and inform each other when a challenge is brought.

In Gavanozov II, C-852/19, the Court held that Articles 6 and 14, read with Charter Article 47, preclude issuing EIOs for searches, seizures or a videoconference witness hearing where the issuing state's law provides no remedy capable of challenging at least the substantive reasons. A system cannot rely on mutual recognition while leaving the affected person without effective judicial protection.

A challenge does not automatically suspend execution. National law governs suspensive effect, but the Directive says suspension should be available under the same conditions as in a similar domestic case. Authorities can meanwhile consult, narrow the request, preserve data without disclosing it, or postpone transfer where necessary.

Does unlawful EIO evidence have to be excluded?

Directive 2014/41 does not harmonise admissibility. Member States apply their evidentiary rules, subject to two EU principles:

• equivalence: an EU-law breach cannot receive less favourable treatment than a comparable domestic breach; and
• effectiveness: the national remedy cannot make protection of EU rights practically impossible or excessively difficult.

The Charter adds effective judicial protection, defence rights, the presumption of innocence and a fair hearing. The remedy must respond to the nature and consequences of the violation. It may include disclosure, an opportunity to cross-examine or obtain expert review, reduced evidential weight, exclusion, retrial or another effective remedy.

M.N. supplies a firm minimum. If the accused cannot effectively comment on information or evidence likely to have a preponderant influence on factual findings, the trial court must disregard it. The Court did not create a broader automatic exclusionary rule for every breach of Articles 6, 14 or 31.

This distinction matters. A missing form field that caused no prejudice is different from secret evidence that cannot be authenticated, privileged material taken without review, or an intrusive measure that lacked the judicial authorisation EU law required. Courts must assess the right infringed, whether the defect can still be cured, the evidence's role and the fairness of the proceedings as a whole without treating seriousness of the alleged offence as a substitute for a remedy.

A practical defence and prosecution checklist

Obtain the EIO and certificate, the issuing or validating decision, domestic legal basis, execution report and custody trail. Identify whether the order sought a new measure or only evidence already held. Compare the requested technique with the issuing state's equivalent domestic conditions and the executing state's execution rules.

Raise issue-stage objections in the issuing state and execution-stage objections in the executing state within each national deadline. Ask the authorities to communicate under the Directive where the file is incomplete. At trial, explain precisely how the defect affected authenticity, confrontation, privilege, privacy or the ability to comment, and identify the national and Charter remedy sought.

Prosecutors should record necessity, proportionality and domestic availability before issue, request only needed data, preserve translations and validation, and disclose enough provenance for effective challenge. Mutual recognition works only when the receiving court can verify the evidence and the defence can contest it.

Conclusion

An EIO carries evidence across borders, not immunity from review. The issuing state controls the reasons and domestic authority for the request; the executing state controls lawful execution and limited refusal; the trial court controls admissibility and fairness. Exclusion is not automatic, but an effective remedy is. Evidence that the accused cannot meaningfully confront and that may drive the factual result must be disregarded.

Sources

• Directive 2014/41/EU on the European Investigation Order, current consolidated version
• Court of Justice judgment in M.N. (EncroChat), C-670/22
• Court of Justice judgment in Gavanozov II, C-852/19
• Court of Justice judgment in Staatsanwaltschaft Wien, C-584/19