On Monday Germany suffered its first 'real' Islamist terror attack, as one analyst put it.
Finance Minister Wolfgang Schäuble said he wasn't surprised, commenting that it was a matter of when not if jihadist terror came to Germany.
But revelations about the prime suspect, Anis Amri, since the attack, which killed 12 people, are leading to serious questions about the competence of Germany's security services.
Armin Laschet, the deputy leader of Merkel's CDU, told Deutschlandfunk on Thursday that revelations about the workings of the security services “can only have unsettled” him.
He has accused investigators in western Germany of washing their hands of the prime suspect, despite knowing he was a danger.
Christian Lindner, leader of the Free Democrats went further, saying “there has clearly been a state failure here that cannot be tolerated.”
Rainer Wendt, head of the German Police Union, has firmly rebuted the accusations
“I find it shameful to talk of a failure on the part of the authorities in the case of Anis Amri – especially when it's a politician like Armin Laschet who does it,” he told the Rheinische Post.
Here are the key facts so far:
What is the evidence against the suspect?
24-year-old Anis Amri's ID papers were found in the cabin of the truck, under the driver's seat.
On Wednesday Süddeutsche Zeitung reported that his finger prints have been found on the door of the truck.
Together these pieces of evidence already appear to build a strong case against the Tunisian.
Why did they only release his name on Wednesday?
One of the main questions being asked is why it took so long to identify him as the prime suspect.
It seemed too good to be true when police said Monday night they had arrested a suspect within an hour of the attack – a Pakistani man who had apparently been identified by an eyewitness.
By the time police let him go late Tuesday for lack of evidence, they had lost 24 hours during which the public had not been told the armed killer was still on the run.
Police say a forensics team only found a wallet containing Amri's papers in the truck cabin on Tuesday afternoon.
It took until Wednesday afternoon for authorities to issue a Europe-wide public wanted notice that gave Amri's full name, age and photograph and warned the public he was dangerous.
Several media outlets have criticized investigators for wasting time on the Pakistani man, even though there were serious questions about his link to the crime from the very beginning.
From early on the fact that his clothes were clean was not meshing with a truck cabin full of blood.
Armin Laschet. Photo: DPA
Could he have been stopped earlier?
If Amri was the attacker, it is now clear he wasn't a so-called “lone actor” that came from nowhere like the axe attacker in Würzburg or the suicide bomber in Ansbach. Both these men, who committed crimes claimed by Isis, were apparently unknown to the security services.
Amri on the other hand seems to have long been recognized as a danger.
Counter-terrorism services in North Rhine Westphalia (NRW) knew he was in contact with radical Islamists and could have been plotting an attack.
Ralf Jäger, interior minister in NRW, admitted on Wednesday that they had previously opened an investigation into Amri on suspicion of planning a terror plot.
He had had contact with Iraqi “hate preacher” Ahmad Abdulaziz Abdullah A., who was arrested by German police in November for setting up a recruitment network on behalf of Isis.
But in February 2016, the Tunisian moved from NRW to Berlin, and a failure in cooperation between detectives in the two states apparently contributed to him falling through the cracks.
Merkel's deputy Laschet accuses NRW authorities of washing their hands of Amri when he left the state.
“We need to look into this, but one things is clear: the source, as so often, lies unfortunately in North Rhine Westphalia,” he said.
“It sounds from Jäger's statement as if they thought that when he went to Berlin there problem was solved, it was Berlin's job now.”
But he also came up on the radar of Berlin authorities.
Prosecutors in the capital say Amri had been suspected of planning a burglary meant to raise cash to buy automatic weapons, “possibly to carry out an attack”.
Surveillance had however shown that Amri was working as a small-time drug dealer, and the observation ended in September.
Amri had used different identities to travel between German states, an unnamed investigator told the Bild newspaper, “but apparently there was never sufficient evidence to arrest him”.
Der Spiegel news weekly said security services had even heard Amri volunteer for a suicide attack – but that he had used a phrase considered too obscure to stand up as evidence leading to an arrest.
But police say Amri's case doesn't highlight incompetence, but an overburdened security apparatus.
Police say that a suspect's 24/7 phone and personal surveillance requires a rotating team of up to two dozen officers. German security services say they are keeping an eye on some 540 radical Islamists they consider potentially dangerous.