From petty criminal to terrorist, Anis Amri, the prime suspect in the Berlin truck attack who was shot dead in Milan on Friday, followed a path similar to that of other jihadists who have carried out attacks in Europe.

The ramming of a truck into a Berlin Christmas market on Monday, killing 12 people and wounding nearly 50, was only the latest example of individual actors hitting soft targets that European police agency Europol described in a report earlier this month as "difficult to predict or foresee, let alone prevent."

But in Amri's case all the warning signs were there, his life of criminality having preceded his allegiance to the so-called "Islamic State" (IS). According to Europol, jihadists committing terror acts in the EU are generally young men who have a criminal past, feel marginalized, and are not strict practicing Muslims, but who have radicalized either through recruiters or on their own.

Path to Germany

Born in the impoverished Tunisian town of Oueslatia, where he was known to drink and take drugs, Amri fled Tunisia in the wake of the 2011 Arab Spring protests, avoiding a four-year prison sentence on charges of robbery and burglary. He arrived in Italy by boat in 2011 at the age of 18, lying about how old he was in order to be considered an unaccompanied minor.

In Italy, he spent four years in prison on arson charges for burning down a refugee shelter. While in prison, he is believed to have become radicalized. Tunisia refused to accept him back and after he was released from prison, Amri made his way to Germany in 2015, as the country experienced an influx of migrants from the Middle East and North Africa.

Once in Germany, he sold drugs and mingled in Islamist circles. He was linked with Iraqi preacher Abu Walaa, who was arrested in November along with others for seeking to recruit fighters for IS. During this time Amri used multiple aliases and continued to avoid deportation to Tunisia because he did not have ID papers.

Warning signs

German authorities had been monitoring Amri on suspicion that he was planning a burglary in order fund a possible violent terror attack. But surveillance was dropped in September 2016 after it was determined he did not pose a security threat. Meanwhile, his deportation was caught up in red tape after his asylum application was denied in July.

"This isn't one of those cases where you look at the guy's background and can't understand why he is a terrorist. He exhibited many signs of someone who could turn to terrorism," said Max Abrahms, a terrorism theorist at Northeastern University in the United States. "This was a preventable attack. This guy should not have been at large."

The warning signs, and belief that the attack could have been prevented, have prompted criticism in Germany over a security lapse, raising questions over the country's ability to handle more than 1 million refugees over the past two years. The influx has sparked security concerns and forced the government to heighten security measures ahead of federal elections in 2017, in which Chancellor Angela Merkel's immigration policies are expected to be a central issue.

Amid the apparent intelligence failure, Merkel pledged on Friday to conduct a "comprehensive" analysis on everything that has gone wrong. "The Amri case raises questions - questions that are not only tied to this crime but also to the time before, since he came to Germany in July 2015," she said. "We will now intensively examine to what extent official procedures need to be changed."

Logistical difficulties

In counter-terrorism, there will always be questions over what is legally allowed in a democracy, as it balances freedom versus security. In the end, it is a political question over how society wants to live. "You don't get complete security and freedom. You need to find balance," a Europol official told DW.

Another aspect is finance and human resources. According to Europol, intensive 24/7 surveillance of a suspect requires at least 20 officers to be available. With hundreds of potential extremists across Europe, surveying one potential terrorist means forgoing following other leads. 

German authorities have foiled several attacks recently. Dozens of alleged Islamists were arrested after a series of IS-inspired attacks carried out by so-called "lone wolf" actors earlier this year. Germany's Federal Prosecutor's Office, which handles terrorism cases, was contacted by DW but declined to comment on whether Amri acted alone or was part of a larger IS cell.