SkyECC Evidence Ruled Inadmissible: A Landmark Decision by the Basel Court of Appeal

Court of Appeal Basel-Stadt

Background: The Basel Court’s Independent Review

The Court of Appeal Basel-Stadt (Appellationsgericht) conducted an independent and thorough review of the admissibility of SkyECC-derived evidence (decision of 3 October 2025 (SB.2023.48). Rather than deferring to the trust principle applicable in mutual legal assistance (Vertrauensprinzip), the court — contrary to the first instance — held that Swiss courts are obliged to scrutinise the lawfulness of evidence gathered abroad, even where foreign authorities have certified compliance with their own law.

Violation of the Territoriality Principle in Cross-Border Surveillance

With the Zurich High Court's decision, the court stated that the MITM technique produced direct effects on Swiss territory: by sending an invisible push notification to each SkyECC handset to extract the cryptographic keys stored exclusively on the device, the French authorities intervened on Swiss soil without mutual legal assistance authorisation. Since the accused's device was located in his Basel bedroom, the operation violated Swiss sovereignty under international law.

The court further stressed that such physical intervention on Swiss territory is not even a prerequisite for a territorial violation. It suffices that a state's actions produce effects on foreign soil — and a violation equally arises where evidence is obtained through means objectively assessed as unfair, in particular by circumventing the rules governing international mutual legal assistance.

Evidence obtained in breach of the territoriality principle is subject to an absolute exclusionary rule — no balancing of interests is permissible (BGE 146 IV 36). The court ordered the SkyECC data to be removed from the case file, sealed, and destroyed (Art. 141 Abs. 5 StPO).

Fishing Expedition: Absence of Individualised Suspicion

The court established that at the time the French surveillance was authorised, there existed no suspicion whatsoever against the accused — let alone the urgent, sufficiently individualised suspicion required under Swiss law for covert surveillance measures. The operation therefore constituted an inadmissible fishing expedition.

Ordre Public and the Limits of Mass Surveillance

Beyond that, the court held that given the severity of the interference — mass surveillance of thousands of users across multiple countries over many months, access to end devices in breach of international law, and the complete absence of any subsequent notification to those affected — the evidence is not merely subject to the relative exclusionary rule and the interest-balancing exercise under Art. 141 Abs. 2 StPO. Rather, the scale and nature of the operation amount to a violation of Swiss ordre public, rendering the SkyECC data absolutely inadmissible regardless of which legal framework governs the admissibility of foreign evidence in Swiss proceedings.

Missing Raw Data and the Right to a Fair Trial

The court identified a further, independent ground of inadmissibility. The data made available to the defence and the court did not consist of raw intercept data but of output generated by the Dutch authorities' proprietary "Toolbox" forensic analysis programme. The Netherlands Forensic Institute itself acknowledged in its validation report that the Toolbox data was not entirely complete compared to the source material on seized handsets, and that only 73.7% of messages had been successfully decrypted.

The court held that the right to a fair trial — rooted in Art. 29 Abs. 2 BV, Art. 32 Abs. 2 BV and Art. 6 EMRK — requires that an accused be in a position to examine how evidence was produced and to challenge potential errors. Because the defence had access only to the Toolbox output relating to the PIN attributed to the accused, and had no means of reviewing the broader dataset to identify exculpatory material or to verify the triage performed by the foreign authorities, the fundamental requirements of completeness of the case file (Vollständigkeit der Akten) were not met. On this ground too, the SkyECC data was inadmissible — a conclusion the court reached going beyond the Zurich High Court's reasoning on this point.

Overall Significance for SkyECC evidence

The Basel-Stadt Court of Appeal thus establishes four cumulative and independently sufficient grounds for the absolute inadmissibility of SkyECC evidence in Swiss proceedings:

1. Violation of the territoriality principle through MITM access to Swiss end devices without mutual legal assistance;

2. Absence of the individualised, urgent suspicion required under Swiss law — fishing expedition;

3. Violation of Swiss ordre public given the scale, secrecy and international reach of the operation;

4. Irreversible compromise of the accused's right to challenge the evidence due to the absence of raw data and the structural impossibility of reviewing the full dataset.

The decision is particularly significant because it squarely rejects the trust principle as a substitute for substantive admissibility review, and because it anchors inadmissibility not merely in procedural rules but in constitutional and Convention guarantees that admit of no interest-balancing override.

You can read the verdict here:

AppGer SB.2023.48.pdf

Download PDF • 1.11MB