An incredulous public has learned that Amri was a rejected asylum seeker and known radical jihadist.
An incredulous public has learned that Amri was a rejected asylum seeker and known radical jihadist with a history of crime who had been under police observation for plotting an attack before surveillance was dropped.
"They knew him. They did nothing," ran the scathing headline of Berlin's B.Z. tabloid.
Here are the missed chances that may have prevented Monday's attack, according to what we know so far from official statements and press reports.
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.
Amri had been watched since March by counter-terrorism services who knew he was in contact with radical Islamists and could have been plotting an attack.
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 the Islamic State group.
Berlin prosecutors 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 in Berlin, 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.
Amid the finger-pointing, debate is raging over whether Amri's case highlights incompetence or 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.
Amri arrived in Germany in July 2015 at a time when a historic influx of migrants and refugees was overwhelming authorities.
His asylum request was rejected in June this year, but Amri couldn't be deported because he had no passport and Tunis denied he was a Tunisian citizen.
Finally, the new Tunisian travel document arrived on Wednesday, two days after the attack, said Ralf Jaeger, interior minister of North Rhine-Westphalia state, who added coolly that he preferred not to comment on the delay.
Germany has repeatedly accused Tunisia and other North African states of stalling on the repatriation of their nationals from Germany.
Adding to the troubling list of questions is the fact that Amri was known as a dangerous offender in Italy and was considered a threat by the United States.
An unnamed US official told The New York Times that Amri had been on a US no-fly list, had in the past allegedly researched online how to build a bomb and had had contact with IS via messaging service Telegram.
In Italy, where Amri had arrived by boat from Tunisia in 2011, he had served more than three years in jail for setting fire to a school building used to house refugees and other offences.
In May 2015, he was placed in deportation detention but released weeks later, free to travel on to Germany, wrote Die Welt.
Italy only issued an alert for him across Europe's visa-free Schengen zone this year, according to Der Spiegel.
When Amri issued his asylum request in Germany, he initially claimed to be an Egyptian fleeing state repression but was unable to answer even basic questions about the country, the magazine said.
His asylum request was denied but, because he couldn't be expelled, he was issued a stay of deportation paper -- the document that police this week found in the mangled truck cabin.