Messenger Surveillance: German Court Limits Police Access to Chat History
In a landmark decision on January 20th, the German Federal Court of Justice (BGH) significantly restricted the powers of investigators regarding the monitoring of encrypted messaging services like WhatsApp, Signal, and Telegram. The ruling clarifies that simply copying existing chat history during surveillance is a violation of applicable law.
Chat Monitoring as “Source TKÜ”
Traditionally, evaluating chat histories was legally treated similarly to telephone monitoring. However, the BGH now classifies accessing a messenger account directly as source telecommunications surveillance (TKÜ). This is the state’s response to finish-to-end encryption, which previously allowed police to intercept messages “on the line.” With end-to-end encryption, direct access to a user’s device is often required, potentially through spy software or, as in this case, a secret “activation” allowing investigators to access an account as an additional device.
Protecting Data Integrity is Crucial
The core of the BGH’s decision lies in the temporal separation of powers. The court argues that source TKÜ should function as an equivalent to classic telephone surveillance, as outlined in the Code of Criminal Procedure (StPO). According to Section 100a Paragraph 1 Sentence 2 StPO, investigators should only have access to data that could have been monitored during the transmission process, explicitly banning retroactive monitoring. The BGH emphasizes that the integrity of an IT system is a valuable asset, and investigators must technically ensure they only capture current communications.
Accessing old messages requires a separate, more stringent process – a secret online search in accordance with Section 100b of the StPO. This differs significantly from source TKÜ, which monitors ongoing communication, while an online search grants access to the entire memory of a target device. Online searches are reserved for investigations into “particularly serious crimes” such as terrorism or murder.
Consequences for the Judiciary: Ban on Evidence Use
The decision has immediate consequences for evidence admissibility. In a previous case, the Aurich regional court convicted a man based on Telegram messages, some written five months before the surveillance order. The BGH declared this evidence unlawful and prohibited its use. Disregarding technical security obligations, the court stated, should not go unpunished, as allowing such evidence would incentivize authorities to circumvent legal limits.
Criminal lawyer Gül Pinar, vice chair of the criminal law committee of the German Bar Association (DAV), described the decision to ARD as “very important and relevant,” stating there had been no legal basis for reading old messages. The BGH’s ruling strengthens fundamental IT rights, protecting the confidentiality and integrity of information technology systems. Pinar noted that thousands of cases previously involved the police evaluating old messages.