The Rasterfahndung: How Counter-Terrorism Shaped German Privacy Law

West German police matched millions of records to find terrorists' hideouts. The method, and two court rulings, shaped German data protection.

12 October 2026 · Part of Cold War — a guide to 19 articles →

In the 1970s the West German Federal Criminal Police Office, the BKA, turned computers on a problem that had defeated its detectives: where do people who live under false names hide? Its answer, the Rasterfahndung or "grid search", compared the records of millions of ordinary citizens against a profile of how a fugitive might behave. The method was born in the hunt for the Red Army Faction, returned after the attacks of 11 September 2001, and was twice reined in by the country's highest court.

A police force that wanted data

In 1971 Horst Herold became president of the BKA, a post he held until 1981. He believed that a modern police force should work like a research institute, and he built up computerised files on persons, objects and events. The Red Army Faction gave him a reason to use them. Its members lived underground, rented flats under invented names and moved between safe houses, so the old methods of watching known contacts brought few results. The group's own statements, which we discuss in our piece on how the RAF wrote its own record, told the police what the group claimed. They did not tell the police where its members slept.

The idea of the grid search was to reverse the question. Instead of searching for a name, the police defined a pattern and let a machine find who fitted it, or, more usefully, who did not fit the pattern of an ordinary resident.

How a grid search works

The logic can be shown with the best-known case, the Frankfurt search of 1979. Investigators reasoned that a person hiding under a false identity would still need electricity, and might pay the bill in cash to avoid a bank trail. Police therefore collected the records of tenants who paid their electricity in cash, a pool that sources put at between sixteen and eighteen thousand people. They then compared these names against the registration offices and other public lists. Most tenants were real residents, and fell away. Those who could not be found in any directory were the interesting ones, since a flat rented under a false name leaves no trace elsewhere.

According to the accounts we have, only two people were left at the end of this process. One of them was a wanted member of the group. Whether the grid search truly produced the arrest is disputed: a critical analysis in the journal of the civil-liberties group CILIP argues that the arrest came from a targeted manhunt, and that how many people went into such searches, how many remained and how many hideouts they uncovered has never been made fully public. The honest summary is that the method has a famous success story and very little audited evidence of effectiveness.

Chronology

The law catches up

The years of the RAF were also the years in which German data protection law took shape, and the two developments were connected. The state of Hesse passed its data protection act in 1970, and the federal law followed in 1977. Both were a reaction to the arrival of computing in public administration, a worry we also describe in our account of the European Commission's contest over computers. Some of the most persistent critics of Herold's methods came from within this new field of law. They asked what it meant for a free state to compile files on citizens who were suspected of nothing.

That question was taken up by a different dispute. In the early 1980s Germans protested against a planned national census, and in December 1983 the Federal Constitutional Court ruled on it. The court held that, under modern conditions of data processing, everyone has a right to decide in principle who may use their personal data, the right of informational self-determination. The census ruling was not about terrorism, but it supplied the vocabulary with which every later grid search was judged. The same decade also saw anxiety about intelligence gathering elsewhere, as in the American debate over NSA surveillance in the Nixon years.

The return of the grid after 2001

After the attacks of 11 September 2001, in which several of the pilots had lived and studied in Hamburg, the German states ordered a new round of grid searches. This time the aim was prevention. The police were not looking for a known fugitive but for so-called sleepers, people who might be preparing an attack while living quietly. The profile was drawn by features such as age, sex, a student status and religion and country of origin, and universities, registration offices and other bodies were asked to hand over records. A civil-liberties review put the number of people whose data were collected and classified nationwide at around 8.3 million.

The results were thin. According to an answer given by the interior minister of Hesse, ten states found no person who could be classed as a sleeper, and in five others the people identified with an Islamist background were already known from earlier investigations. Only in Hamburg were contacts and suspected supporters of the attackers found. A study by the Max Planck Institute for criminal law treated the post-2001 search as the only nationwide use of the preventive grid search of its kind.

The court sets a limit

One of the people affected, a student in North Rhine-Westphalia, took his case to Karlsruhe. In its order of 4 April 2006 the Federal Constitutional Court held that a preventive grid search interferes seriously with informational self-determination. It is compatible with the constitution, the court ruled, only if there is a concrete danger to high-ranking legal interests such as the life or freedom of persons or the existence of the state. A general threat situation, such as the one after the attacks of 2001, or tensions in foreign policy, is not enough.

The ruling did not ban the method. It made it a tool for emergencies with specific evidence rather than a routine tool of suspicion, and it showed that the principles worked out in 1983 still bound the police a generation after the RAF's peak.

What the story shows

The grid search is an episode of the Cold War era that has outlived it. It began when a democratic state under attack, at the time of the events described in the German Autumn of 1977 and the Stammheim trial, looked for an answer in technology. Our record of these operations shows how many of the group's attacks went unsolved, which helps to explain why the police were drawn to an instrument that promised to find people nobody could name. The later years, in which the third generation produced almost no convictions, only strengthened that pull.

Conclusion

The grid search left two legacies. It gave the German police a model of data-driven investigation that other countries later copied under other names. And it gave the German constitutional order a body of case law that treats personal data as something citizens hold against the state, even in the shadow of terrorism. The evidence that it caught terrorists is limited and disputed; the evidence that it forced the law to define its limits is not.

Frequently asked questions

What does Rasterfahndung mean? The word means a "grid search" or dragnet investigation. Police compare large sets of personal data, such as utility or registration records, against a profile to filter out the few people who match it.

Did the Rasterfahndung catch members of the Red Army Faction? The best-known case is the Frankfurt search of 1979, which is said to have left two people, one of them a wanted member of the group. Critics dispute that the arrest was a result of the grid search, and the full results of such searches were never published.

Why did the Constitutional Court restrict it in 2006? The court found that a preventive grid search interferes seriously with the right to informational self-determination. It allowed it only where a concrete danger to important legal interests exists, not merely a general threat after 11 September 2001.

How many people were screened after 2001? A civil-liberties review put the figure at around 8.3 million people nationwide. According to the Hessian interior ministry, most states found no sleepers, and the study rests on official replies and press reports.

As an Amazon Associate I earn from qualifying purchases. Affiliate links in Recommended reading — and in Further reading on older articles — may earn Writesides of History a commission at no extra cost to you.