The suicide mission on Breitscheidplatz stunned Germany. It is now harder for Germans to walk around Christmas markets and folk festivals. The attack has shaken the supposed certainty that Germany's antiterrorism defense works. Now many Germans doubt that this finely differentiated capillary system of German federalism, with its 36 police and intelligence services, is the best of all solutions. In Anis Amri's case, this system and the state failed.

How could this happen? And how can such a mistake be prevented in the future?

Over three months, a team of ZEIT journalists has investigated the attack and its prehistory. Reporters have traveled to Tunisia to Amri's family, to Italy, where Amri stepped onto European soil for the first time, and to Poland for the funeral of the truck driver Łukasz Urban. They analyzed several thousand pages of investigations, observation logs and intelligence records from Germany and Morocco, where the authorities were particularly concerned about Amri's proximity to IS. In addition, ZEIT spoke with the Germany's Federal Minister of Interior, Thomas de Maizière (CDU), and his North Rhine-Westphalian colleague Ralf Jäger (SPD), as well as with investigators from state-level and federal authorities, some of whom attended the decisive meetings.

The research reveals a picture of a security apparatus that was rebuilt after September 11, 2001, but whose architecture fits today's reality quite poorly.

On the morning of February 18, 2016, the day after the GTAZ meeting, Anis Amri threw two rucksacks over his shoulder in Dortmund, where he had stowed his belongings, bought a ticket and got on the long-distance bus to Berlin. At the same time as the bus left Dortmund, the police officers from North Rhine-Westphalia asked their colleagues in the capital to monitor Amri. The Berliners decided otherwise: They picked up Amri at the central bus station, took him to the criminal investigations office, photographed him, took his fingerprints, and confiscated his mobile phone. The Düsseldorf police were livid: the Tunisian had been warned.

For dangerous persons such as Amri, in other words persons whom the authorities view as violent, the BKA isn’t responsible, but rather the respective state (Land in German) authority where the person resides. Responsibility for Amri therefore was at times in North Rhine-Westphalia, at others in Berlin, depending on where he was located.

And Amri moved around a lot: from the small town of Emmerich on the Rhine to Dortmund and then to Oberhausen, to Berlin and back again, from the mosque to acquaintances and back to the mosque again. Whenever it appears that he had changed states, the state-level police authority (LKA) in North Rhine-Westphalia shifts responsibility to Berlin, and vice versa. When studying the files, one gets the impression that every time he moved location, there was a sigh of relief from an office in the state he just left.

In early March 2016, the investigators analysing Amri's cell phone date stumbled upon a conversation he had on February 2 with two Islamists on the chat program Telegram. The two men used Libyan cell numbers and were apparently near the Libyan town of Sirte. He wants to marry one of their sisters, said Amri. When his counterpart did not immediately understand, he whispered, it's about dugma, which in the Islamist scene means "trigger." According to BKA, the word is used by Islamists as a synonym for a suicide attack.

But then his interlocutor got it. Amri should not use the word again, the man reprimanded him in an audio message that he then sent. They agreed on a code: Amri should communicate to a contact person in Germany that he wants to "serve the religion of God no matter what means." The man will bring him to another brother "and direct him." And be careful on the telephone, the man in Libya warned. Don't call home as the Tunisian authorities are on alert. Shots can be heard in the background. God will unite them in paradise, said the man, whose number Amri stored under an entry: "Malek-ISIS."

When the investigators listened to the audio files on Amri's mobile phone, they noted: Amri announced "in a roundabout way that he is in Germany to commit a suicide attack."

At the latest, in March 2016, it should have been clear to all parties that the undercover agent wasn't talking nonsense, and that the assessment of the North Rhine-Westphalian police officers was correct, not the BKA's. Amri was not only a supporter of IS, but also well networked. And above all: determined.

The two men in Libya, with whom Amri chatted, were Tunisians. Perhaps Amri knew them from home. In Emmerich, in the refugee shelter, he had passed around pictures of black-clad fighters. These were relatives, he claimed at that time: cousins, an uncle, allegedly all with IS.

What kind of family is he from? Did his radicalization begin in Italy and Germany, or before in Tunisia?

A criminal in Tunisia and Italy

"At home, Anis was, above all, a spoiled mommy's boy," says Walid Amri, 30, one of Anis's older brothers. The family had four sons and five daughters. Anis had been given everything he wanted in a modest way, says Walid. As ZEIT interviewed him, he sat in a cafe on the edge of a sheep pasture, about one hour’s car ride south of the capital Tunis. The waiter served us green tea with mint syrup.

In the days after the attack, under the spotlight of world publicity, the family was made out to be a terrorist clan. Walid Amri says he does not want to go down in history as the "brother of the terrorist." He is a courteous man who leads a quiet life and earns his money by transporting cattle feed.

Their mother, Walid said, regularly asked them to give Anis a bit of money. Anis had surrounded himself with false friends, smoked hash, and stolen a car. But the police caught him. "He was a criminal," Walid says. In Tunisia, he would have been incarcerated.

In 2011, Anis Amri had just turned 18. He used the turmoil of the Tunisian revolution to escape the law. He scraped together the money for the human smuggler who brought him to the Italian island of Lampedusa. He called his family from a payphone in an Italian detention center. A little later, a court in Tunis handed down a sentence of four years imprisonment.

If you believe his brother, then Anis Amri was a young man straying, spoiled and without plans, but not a terrorist. Only in Europe did he get into the hard stuff: cocaine, amphetamines, hate.

Anis Amri knew that he'd never be recognized as a refugee in Europe, says his brother. "His plan was to collect as much money as possible, and then return to Tunisia," says Walid. The family even hired an attorney to get Anis Amri's prison sentence reduced -- to help him start off on a new foot in the old homeland.

Perhaps Amri's radicalization began in Tunisia, even if his brother and his parents don't want to hear it. Amri’s relationship to his nephew, Fadi, who is now sitting in the high-security prison in Tunis, suggests this. He is suspected of having known about the attack in Berlin. Until shortly before the Breitscheidplatz attack, messages had been exchanged between the two of them. The thesis of an early radicalization is supported by the Moroccan secret service. According to it, Amri had already tried to join IS in Tunisia, for which he was wanted by the Tunisian authorities.