Updated

The Berlin terror suspect who repeatedly slipped through the fingers of German authorities was reportedly on the U.S. no-fly list months before Monday's deadly attack.

German officials on Thursday continued to hunt Anis Amri, who is considered armed and dangerous. A fingerprint in the cab of the truck used in Monday's attack was found on Thursday to belong to Amri.

Amri piqued the interest of U.S. officials after it was discovered he had researched the construction of explosive devices and communicated with ISIS leaders on at least one occasion via the group’s Telegram Messenger, officials told The New York Times.

ATTACK PROMPTS HIGH SECURITY IN U.S. CITIES

But while the U.S quickly moved to keep Amri out of the country, Germany couldn’t get him to leave.

There were red flags galore surrounding the Tunisian-born Amri:

  • Amri, 24, left Tunisia in 2010 after stealing a truck, a crime for which he was sentenced to prison time in absentia, Die Welt reported.
  • He arrived in Italy but couldn’t stay out of trouble, eventually landing in an Italian prison for setting fire to a school at a refugee camp, according to an interview with Amri’s father broadcast on a Tunisian radio station. News agency Ans reported the fire was part of a revolt against “infidels.”
  • Amri was transferred among several Sicilian prisons for bad conduct, The Associated Press reported. Prison records show he bullied fellow inmates and attempted to spark insurrections.
  • Amri applied for asylum in Germany in July 2015 and was denied in June 2016; however, he was never deported. Tunisia first claimed it could not find evidence he was a citizen of the country and then delayed in sending him a passport, German officials said. 
  • Germany had hoped to deport Amri after learning he was plotting a “serious act of violent subversion,” an official told The Washington Post.
  • Amri was reportedly arrested in Germany on at least two other occasions after his asylum rejection, however, he was released each time.
  • German officials monitored Amri’s connections to extremists, and at one point investigators believed he may have offered himself as a suicide bomber, Der Spiegel reported. But due to Amri’s ambiguous statements, Germany was never able to arrest him.
  • Authorities began investigating Amri in March but ended the operation in September despite uncovering some troubling connections. He had lived with a suspected Islamic extremist and was allegedly a follower of an Iraqi-born German preacher who was later arrested due to connections to ISIS.
  • Officials again convened in November to share intelligence that Amri was connected to Islamist militants. A month later, Amri killed 12 people and wounded 48 when he drove a truck into a crowd at a Christmas market.

“This is the smoking gun to show that the vetting process has major gaps in it, that intel is not being shared, that information about ideological extremism is not being adequately considered,” said Ryan Mauro, a National Security Analyst for the Clarion Project. “It shows that ideology is not playing a strong enough role in the vetting process, even in Europe.”

The failure of German authorities to catch Amri before the ISIS-claimed attack mirrors their current struggle to capture the fugitive after the fact.

Amri wasn’t identified as the prime suspect until Wednesday, despite leaving a wallet with identification papers behind in the truck he used during the rampage. In the first two days after the attack, Germany detained and questioned two other people, but had to release both due to insufficient evidence.

But Sebastian Gorka, author of "Defeating Jihad," placed the blame on the liberal policies of the German government, which allowed an influx of nearly a million asylum-seekers into the country around the time Amri entered.

“Looking into what we know already, it’s less a function of bad vetting – it’s bad policy," Gorka told FoxNews.com

“The facts are, the red flags were there but the policies of Berlin were such that the individual was released. He wasn’t deported…That is a function of policy, not policing.”

Gorka said police were already fighting an uphill battle thanks to the country throwing open its borders to migrants.

“The politicians have endangered their fellow Germans, not the policemen," he said. "It’s easy to blame the operators, but the real responsibility lies with the politicians.”

Two Americans were victims of the Monday massacre, and one of the unidentified individuals remained hospitalized on Thursday, the U.S. Embassy told Fox News. An update was scheduled for later in the day.

Fox News’ Greg Palkot contributed to this report.