Berlin - Breitscheidplatz now resembles a high-security zone. It's surrounded by bollards and steel baskets filled with sandbags - measures intended to prevent a repeat of the terrorist attack of 19 December 2016. 

Four years ago this Saturday, Anis Amri, a Tunisian, hijacked a tractor trailer, shot its driver and then, approaching from Hardenbergstraße, drove into the middle of the Breitscheidplatz Christmas market, killing 11 people and injuring more than 60, many of them seriously.

A memorial on the steps of the Gedächtniskirche at Breitscheidplatz commemorates the victims. The names of the dead are inscribed on the steps.

But the temporary truck barriers on the square indicate that the wounds inflicted by the attack are far from healed. The fact that two committees are investigating the attack - in the Bundestag and the Berlin parliament - shows that much is still unknown about the crime. The further the tragedy recedes into the past, the more strange things come to light. And the clearer the extent of the authorities' failures becomes.

Photo: dpa/Bernd von Jutrczenka
A trail of devastation: the truck that Anis Amri piloted through the Christmas market.

That's the impression that the Bundestag committee gives, at least. On Thursday, Hans-Georg Engelke, an interior ministry official, testified. In the evening, former interior minister Thomas de Maizière (CDU) was questioned. At the time of the attack, de Maizière was in charge of Germany's federal security services. The parliamentarians questioned whether he then had had a grip on the Federal Office for the Protection of the Constitution (Verfassungsschutz, Germany's domestic intelligence service).

The agency had an informant in the Fussilet mosque in Berlin's Moabit neighbourhood where Amri was a known visitor and, in January 2016, sent an official report to several other German security authorities, including the Berlin LKA (Landeskriminalamt). It indicated that Amri was planning a robbery and wanted to use the money to buy Kalashnikovs (AK-47s) for terror attacks. But these tip-offs weren't consistently followed up. Rumours that Amri himself was a Verfassungsschutz source were also never dispelled.

On 10 December, the Verfassungsschutz of the state of Mecklenburg-Western Pomerania caused a stir. An informant there had claimed that an Arab gang had helped Amri escape the scene of the crime. About two months after the attack, the informant from the Islamist scene had reported to his handler that he had overheard gang members talking about Amri in Berlin. From this, he concluded that they had given him money and helped him flee the city.

The head of the intelligence agency in Mecklenburg-Western Pomerania, Reinhard Müller, considered the tip to be false and did not pass it on to the federal authorities. The information was "incoherent in itself", he explained to the committee. Yet his office had been obliged to pass on such information to the federal investigating authorities - regardless of how valuable the Islamist's tips may have seemed, said Germany's attorney general, Peter Frank.

Why was Amri's phone stuck in the truck's radiator grille?

In November, the founder of the rightwing protest movement Pegida, Lutz Bachmann, was called as a witness by the Bundestag committee. Shortly after the attack, Bachmann wrote on Twitter that the attacker was a "Tunisian Muslim." At that time, the identity of the attacker was supposedly unknown, because, according to the official record, Amri's identity papers were only found later in the truck. Bachmann said he had received an anonymous call 40 minutes after the attack with details about the perpetrator.

The caller had used a Berlin dialect and identified himself as a local cop. He allegedly told Bachmann that the attacker was Tunisian. Bachmann says he then received a text with the same information - from an internet service that can be used to send text messages anonymously. Some members of the committee have wondered for some time whether Amri's identity card might have been found in the truck earlier.

Questions upon questions. What also remains unanswered is why there was no glass dust on the wallet containing Amri's immigration papers, which were found in the truck's cab and used to identify him. The vehicle's windows shattered on impact, and glass dust covered almost everything in the cab. Amri's fingerprints were not found on the wallet either.

Even stranger: a flip phone that Amri is said to have used was discovered in the driver's cab - also without his fingerprints. Amri's second mobile phone, which he allegedly used to chat with a friend on the way to Breitscheidplatz, was found stuck in the radiator grille of the truck. How it got there, the detective superintendent who was responsible for securing the crime scene could not explain to the committee.

BKA chief Holger Münch: Resources were scarce

"I'm hearing about it for the first time today," he said.

Heads of security agencies also testified before the committee, such as Bruno Kahl, president of the BND, Germany's national intelligence service. The agency had received information from Moroccan intelligence about Amri's Salafist activities. The BND failed to pass the tip on to the Verfassungsschutz. Kahl has admitted that this was a mistake.

The BND had received several videos from foreign intelligence services. One of them showed Amri with a gun at another location. The BND did not pass the material on to the Federal Criminal Police (BKA) because it considered it irrelevant. Nowadays, the agency follows the principle of "when in doubt, pass it on", says Kahl. He admitted that there had been communication errors among authorities prior to the attack.

Holger Münch, head of the BKA, told the committee that the German police are still searching for a Tunisian who allegedly guided Anis Amri via chat from abroad. It is also still unclear where Amri obtained the pistol and how he was able to leave Berlin after the attack. Münch referred to the security forces' scant resources, which had been unable to keep pace with unfolding events.

Photo: Volkmar Otto
The victims of the attack are commemorated in front of the Kaiser Wilhelm Memorial Church.

Some members of the parliamentary committee are of the opinion that the BKA should have taken over the investigation of the terrorist-to-be instead of the state criminal investigation offices (LKA) in Berlin and North Rhine-Westphalia. At least in part because he moved between several states. Münch said that there had been no request from a state to take over the investigation. Besides, he added, the BKA was working at full capacity at the time.

Time and again, the authorities suggested that Amri had acted as a lone wolf. MPs in the parliamentary committee have come to the conclusion that he was part of a network. Now, the attorney general, Peter Frank, also says that neither he nor his office had assumed that Amri was a lone wolf. Amri had been in contact with a Tunisian ISIS fighter by phone during the crime, Frank told the committee on 10 December.

Among the many inconsistencies is the fact that various witnesses claim to have seen people fleeing from the cab in different directions. A video sequence shows a fight immediately after the attack. A man was seriously injured by a blow when he tried to stop the fleeing attacker.

Witnesses also say they saw a blue-gloved first responder get out of the truck after the attack. He allegedly looked like Amri's closest friend Bilal Ben Ammar. Amri is said to have previously scouted out the crime scene with Ben Ammar. However, a senior public prosecutor at the federal supreme court had already asserted before the committee last year that the suspicion of Ben Ammar's complicity had not been substantiated. Besides, Ben Ammar can no longer be questioned since he was hastily deported to Tunisia on 1 February 2017, just a few weeks after the crime.