Messenger chat logs and encrypted message history have become central to criminal proceedings, raising complex questions about fundamental rights and evidence admissibility. According to recent rulings by the German Federal Constitutional Court (Bundesverfassungsgericht) and the Federal Court of Justice (Bundesgerichtshof), state access to messaging data through source telecommunications surveillance faces strict constitutional limits to protect privacy and IT confidentiality.
Law enforcement agencies rely on specific statutory provisions within the German Code of Criminal Procedure (StPO) to secure and evaluate digital communications. Under sections 94, 95, and 98 of the StPO, police and prosecutors can seize physical devices such as smartphones and laptops during authorized searches. Furthermore, section 100a of the StPO governs the real-time monitoring of ongoing telecommunications. This framework includes source-based telecommunications surveillance (Quellen-TKÜ), which allows authorities to use technical tools to intercept encrypted messenger data directly at the source.
These investigative measures interact directly with constitutional protections. Article 10 of the German Basic Law (Grundgesetz) guarantees the privacy of correspondence, posts, and telecommunications. Additionally, the jurisprudence of the Federal Constitutional Court derives a fundamental right to the confidentiality and integrity of information-technology systems from Article 2 paragraph 1 in conjunction with Article 1 paragraph 1 of the Basic Law. These provisions establish high hurdles for state intrusion into personal digital environments.
Constitutional Safeguards and the ‘Trojaner II’ Decision
In its decision dated June 24, 2025 (1 BvR 180/23), known as the “Trojaner II” ruling, the Federal Constitutional Court refined the constitutional requirements for source-TKÜ measures. The court established that deploying state malware to infiltrate an information-technology system constitutes a particularly severe infringement on fundamental rights. According to the court, such measures are permissible only when investigating sufficiently serious crimes, when milder means are inadequate, and when the statutory provisions are clear, precise, and technically controllable.
A central pillar of the ruling is the protection of the core area of private life (Kernbereichsschutz). The state is barred from harvesting intimate communications that touch upon the innermost sphere of personal life. Because certain technical monitoring tools cannot be completely controlled, the Federal Constitutional Court mandated strict deletion and documentation obligations. Investigators must technically restrict data collection so that only content relevant to the specific criminal proceedings is recorded.
Retroactive Telegram Chats and Evidence Exclusion
The Federal Court of Justice addressed the limits of retroactive chat collection in a decision on January 20, 2026 (3 StR 495/25). The case involved a source-TKÜ measure targeting a Telegram account where investigators not only monitored communications from the time of the judicial order but also extracted chat histories retroactively from the months preceding the order.
The Federal Court of Justice classified this retroactive retrieval as a form of source-TKÜ under section 100a of the StPO. The court emphasized that the statute is technically designed to collect content only from the time of the order onward. Because the unauthorized collection of older messages violated the statutory framework and the constitutional protection of IT systems, the court declared the retroactively gathered Telegram chats inadmissible as evidence in the proceedings. This precedent demonstrates that exceeding the temporal limits of an authorized surveillance measure triggers a legal prohibition on the use of that specific evidence.
Procedural Safeguards and Defense Strategies
The legality of obtaining chat logs depends on strict adherence to judicial reservation requirements outlined in section 100e of the StPO. Investigative measures require prior judicial approval, except in exigent circumstances where a prosecutorial order may be used for seizure. Defense practitioners regularly examine whether seizure orders and surveillance warrants contain sufficient justification, whether they properly delineate the timeframes and specific communication channels involved, and whether judicial oversight was maintained.
Defendants facing investigations involving digital evidence retain fundamental procedural protections, including the right to remain silent and the right not to surrender access codes or passwords to seized devices. As jurisprudence continues to define strict boundaries for digital surveillance, the legal assessment of chat messages requires careful evaluation of technical implementation, statutory compliance, and constitutional safeguards.
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