Communication surveillance and the seizure of letters in criminal proceedings are state investigative measures that intervene deeply in privacy and the confidentiality of communication. They enable authorities to monitor, evaluate, or secure messages, communication data, and mail belonging to an accused person.

This specifically includes telephone calls, emails, messenger messages, and other digital data transmissions. The seizure of letters includes the opening and withholding of physical or electronic mail. In addition, there are graduated measures such as information on subscriber and access data, the collection of traffic data, or the localization of technical devices.

A specific suspicion of a crime, a comprehensible investigative purpose, and a proportionate limitation of the measure are required. A clear tiered model applies. The more deeply authorities intervene in communication and private life, the more precisely the purpose, scope, and duration of the measure must be justified.

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Difference Between Simple and Intensive Investigative Measures

In criminal proceedings, authorities work with a clearly graduated system of interventions. Not every measure interferes with the rights of an accused person to the same extent. This is precisely where the decisive difference lies.

Simple investigative measures primarily concern external data of a communication. This includes, for example, name, address, or technical assignments such as an IP address. The content of the communication remains untouched and is therefore permissible even in the case of a specific initial suspicion.

Intensive investigative measures go significantly further. They concern the content of messages or enable comprehensive monitoring of behavior. This includes, in particular, reading messages or intercepting conversations. These measures directly intervene in privacy and fundamental rights.

The system follows a clear principle:

• The lesser the intervention, the lower the legal requirements
• The more severe the intervention, the stricter the legal hurdles

A clear tiered model applies to investigative authorities: Authorities may not immediately resort to the most severe measure. They must always check whether a milder measure is sufficient to clarify the facts. Only if that is not the case is more intensive surveillance considered.

Seizure of Letters

The seizure of letters allows authorities to secure or open mail belonging to an accused person. This does not only affect traditional letters. Packages or electronic mail can also fall under this.

The measure directly intervenes in the secrecy of correspondence. Therefore, strict requirements apply. The measure requires the investigation of an intentionally committed criminal offense with a threatened penalty of more than one year.

A seizure of letters often serves to:

• Secure evidence
• Uncover agreements between parties involved
• Locate documents or assets

Criminal proceedings follow the principle of proportionality. A seizure of letters is therefore only considered if milder measures are not sufficient.

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Information on Subscriber and Access Data

The request for subscriber and access data does not concern the content of a communication. Authorities only receive the technical assignment of a connection or user account to a specific person.

This specifically includes personal identification data such as:

• Name and address of a user
• Telephone numbers and user IDs
• Public IP addresses including time allocation
• Assignment of email addresses to specific users
• User IDs for communication or online services

With this information, investigators can determine which person is behind a specific connection or online account. Without the assignment of technical access data, many internet crimes can hardly be attributed to a specific person.

At first glance, the intervention appears less intensive than communication surveillance. Nevertheless, this data request also affects privacy. Even technical usage data often allows for far-reaching conclusions about contacts or online activities.

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Information on Message Transmission Data

The request for message transmission data goes significantly further than a simple subscriber data query. Authorities receive so-called traffic and connection data.

This makes it possible to trace:

• who communicated with whom
• when a connection took place
• how long the communication lasted
• from which location the communication occurred

The content of the messages remains fundamentally untouched. Nevertheless, the measure often enables a very precise analysis of social contacts and movement patterns. This is precisely why it already represents a significant intervention in fundamental rights.

The measure is frequently used in investigations involving organized crime, fraud offenses, or drug trafficking. In some cases, the law requires specific facts from which it follows that data of the accused can be determined as a result.

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Localization of Technical Equipment and Occasion-Related Data Retention

The localization of technical equipment allows investigative authorities to determine the location of a mobile device. This primarily affects mobile phones, tablets, or comparable communication devices.

Even without access to message content, location data often provides a surprisingly accurate picture of a person’s movements, contacts, and locations. Investigators can thus trace whether an accused person was at a certain location or met with other parties involved.

Investigative authorities can thereby trace locations, movement profiles, or contacts between parties involved.

In addition, the Code of Criminal Procedure recognizes so-called occasion-related data retention. In occasion-related data retention, the deletion of certain data is temporarily suspended so that investigative authorities can access it later.

Since location data can deeply intervene in privacy, the law requires sufficient suspicion of a crime as well as a comprehensible justification for the measure.

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Surveillance of Messages as the Most Intensive Intervention

The surveillance of messages enables authorities to access the content of ongoing communication. This specifically affects telephone calls, messenger messages, emails, and comparable digital forms of communication.

The measure enables direct insights into personal communication and confidential conversations.

Therefore, the Code of Criminal Procedure only allows this measure for intentionally committed criminal offenses with a prison sentence of more than one year. This includes, for example, organized crime, terrorism, serious drug trafficking, or extensive white-collar crime.

Surveillance fundamentally requires judicial authorization. The authorities must precisely define the scope of the measure. Unlimited or blanket surveillance is inadmissible.

If the legal requirements no longer apply, investigators must terminate the surveillance immediately. This applies in particular if the suspicion of a crime is not confirmed or if milder measures are sufficient.

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Substantive Requirements for Investigative Measures

Investigative measures require certain legal prerequisites. Authorities may not use surveillance measures for general control or mere information gathering.

The focus is initially on the suspicion of a crime. Investigators must provide a comprehensible explanation as to why a certain person is to be linked to a criminal offense. Mere assumptions are not sufficient.

A necessary prerequisite is the necessity of the measure. Authorities must check whether the facts can also be clarified with less intrusive means.

Proportionality is also crucial. The more intensively a measure intervenes in fundamental rights, the stricter the legal requirements are.

This is precisely why the Code of Criminal Procedure treats simple data requests differently than the surveillance of message content.

Formal Requirements and Judicial Authorization

Many surveillance measures may not be ordered by the police alone. The Code of Criminal Procedure often requires judicial authorization. The court thereby checks whether the legal requirements are actually met before the measure is carried out.

Particularly strict requirements apply to the surveillance of messages. Investigators must specifically demonstrate to the court:

• which criminal offense is being prosecuted
• why there is a strong suspicion of a crime
• why the measure is necessary
• why milder means are not sufficient

The court then checks whether the legal requirements are actually met. Without sufficient justification, the measure may not be authorized.

For less intensive measures, lower requirements sometimes apply. For information on subscriber and access data, a specific suspicion of a criminal offense is sufficient.

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Role of the Public Prosecutor’s Office and the Court

In preliminary proceedings, the police, public prosecutor’s office, and court work closely together. Nevertheless, these bodies perform different tasks.

The police carry out investigations in practice. They secure evidence, evaluate data, and implement ordered measures. The public prosecutor’s office leads the preliminary proceedings and decides which measures should be requested.

In the case of intensive interventions in fundamental rights, the court checks the admissibility of the measure. This particularly affects:

• Communication surveillance
• Localization of technical devices
• Seizure of letters
• certain forms of data evaluation

This creates a multi-stage control system. Investigative authorities may not carry out severe interventions independently and without limit.

Judicial control is intended to ensure that surveillance measures are only used if the legal requirements are actually met.

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Rights of the Accused in Preliminary Proceedings

Even during ongoing investigations, an accused person retains their rights of defense and fundamental rights. Investigative measures may therefore not be carried out without limits.

Those affected have, in particular, the right to:

• legal defense
• inspection of files to the extent permitted by law
• review of judicial decisions
• protection against disproportionate interventions

Subsequent control plays an important role, especially in the case of surveillance measures. Courts must check whether investigators have complied with the legal requirements and whether the measure was actually necessary.

If data was collected unlawfully, this can have significant consequences for the criminal proceedings. Under certain conditions, such information may not be used as evidence later.

For the accused, an early legal review is particularly important. Surveillance measures often intervene deeply in privacy and frequently affect large amounts of personal data.

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Admissibility of Evidence and Nullity of Unlawful Measures

Surveillance measures may only take place within the legal limits. If investigative authorities violate these requirements, this can have significant consequences for the criminal proceedings.

Surveillance without judicial authorization or without a sufficient legal basis can be unlawful. The same applies if authorities exceed the scope of surveillance or evaluate data without a permissible purpose.

Not every procedural error automatically leads to the inadmissibility of evidence. The Code of Criminal Procedure distinguishes between mere formal errors and serious legal violations. The decisive factor is often how strongly the measure intervened in fundamental rights and which regulations were violated.

Particularly in the case of surveillance of messages or extensive data evaluations, courts check very carefully whether the legal requirements were actually met. Missing authorizations, insufficient justifications, or disproportionate interventions can lead to certain results not being allowed to be used later.

Your Benefits with Legal Assistance

Surveillance measures often take place in the background. Many of those affected only find out late that authorities have monitored messages, evaluated data, or localized technical devices.

This is precisely why an early legal review is crucial. Investigative measures according to §§ 134 ff StPO often intervene deeply in privacy and regularly affect large amounts of personal data.

Legal representation helps in particular to:

• check the legality of the measure
• monitor judicial authorizations
• point out disproportionate interventions
• challenge inadmissible evidence in a timely manner
• build defense strategies early on

Especially in the case of communication surveillance or extensive data evaluations, the preliminary proceedings often decide the further course of the criminal trial. Missing authorizations, exceeded surveillance periods, or inadmissible data evaluations often only become apparent upon close inspection of the files.

An early defense not only protects procedural rights. It can also be decisive for which evidence may be used at all later.

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FAQ – Frequently Asked Questions

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