BERLIN — One recent underreported case of a 24-year-old Afghan in Germany is a perfect example of how hard it is for security authorities to track potentially dangerous Islamists. The suspected radical, who has disappeared near Hannover in Lower Saxony, had previously traveled to Afghanistan to be trained in the handling of explosives. Since July 2015, he has been registered as "presumably dangerous."

There are two sentences that have been repeated over and over, like a mantra, by police investigators and domestic security agents. "It's just a matter of time before there will be a big attack"; and"it's almost sure that we will already know the culprit." Of course, on Dec. 19, these two dark prophecies became a brutal reality. Anis Amri, the alleged culprit in the Christmas market truck attack in Berlin, certainly didn't "come out of nowhere" for German authorities, as it had apparently been the case in relatively smaller attacks last year in Frankfurt, Würzburg or Ansbach. Since last February, the Tunisian-born had been labeled as: "presumably dangerous'. They knew that he'd kept company with Islamists, visited mosques with extremist elements and hung around with ISIS sympathizers. And they knew about his intentions to commit an assault.

This particular case illustrates the difficulties when it comes to dealing with extremists who wouldn't be put past committing an assault at any moment: While several thousands of Islamists are estimated to be possible threats, 549 have been officially labeled as "presumably dangerous." To effectively keep them all under close control is practically impossible with today's prevailing legal framework.

Indeed, the other case of the similarly registered "dangerous' 24-year-old Afghan from the Lower Saxony state in northern Germany makes this very clear. Known by the alias, Ahmed A. and born in Kabul, the suspect arrived in Germany in November 2011. Quickly, the authorities understood that they were dealing with a radical Islamist. What's particularly controversial is that in the asylum seeker's file were documents concerning the "training for handling explosives' information, as well as a certificate of appreciation of the U.S. army, for helping with the mine clearance and the ordnance disposal in Afghanistan. One thing's for sure: Ahmed A. knows a lot about explosives.

The Federal Office for the Protection of the Constitution eventually got tipped off that the man with this identity might be planning a suicide attack, possibly against NATO soldiers in Afghanistan. Consequently, in July 2015, the State Office of Criminal Investigation in Lower Saxony immediately classified him as an "presumably dangerous' person, "type: actor."

What followed were numerous attempts to get and keep the Islamist under control. First his piece of identification was retrieved, in order to prevent any travel activity. Ahmed A. appealed that decision, in vain, and went to Berlin, obtaining an Afghan passport at that country's consulate, which too had immediately been collected by the authorities.

Time bomb

On February 8, 2016 he was then deprived of the status of refugee. He was then — just like Berlin attacker Anis Amri — obliged to leave the country. But no deportation was initiated. Why? "Assault intent abroad," cited a report. Ahmed A. was allowed to stay — despite, or rather because, of the danger he posed to troops in Afghanistan.

That he was considered a ticking time bomb became very clear in April, when US President Barack Obama visited Hannover, the Lower Saxon capital. During that time, Ahmed A. had been monitored by a mobile task force 24/7. On top of that, he had reporting obligations, required to present himself at the police station on a regular basis. The last time he did so was in July. Since then, Ahmed A., a trained potential suicide bomber, has gone missing.

For Jens Nacke, a Lower Saxony legislator, the details of this case amount to a politico-security fiasco. "Lower Saxony desperately needs a paradigm shift when it comes to domestic security," he says.

The term "presumably dangerous' was first introduced by the German Federal Office of Criminal Investigation in 2004. It is not a legal identification. Per definition, it designates a person who "is likely to commit a politically motivated crime on a large scale". Meaning: They aren't criminals, but might very well become one. As a result, police face tremendous legal obstacles when dealing with them.

In the wake of the Berlin attack in December, which killed 12 and injured 56, Germany's federal government now wants to significantly step up their anti-terrorist controls. This would include a central registering and processing of all potentially dangerous individuals through the Federal Criminal Police office. Interior Minister Thomas de Maizière has also expressed support for detention and deportation of non-German Islamists, including the use of electronic monitoring ankle bracelets.

Such supervision with the help of tracking devices would be possible, but some wonder if it really helps preventing attacks. Also faster deportations of foreign extremists are theoretically imaginable. In Italy for instance, on average two Islamists per week are expelled from the country that way. In Germany that was often hindered by complicated bureaucracy or missing agreements with third-states. The Berlin culprit Anis Amri should have been deported, after his application for asylum had been rejected. But the Tunisian authorities did not issue any replacement documents for the Islamist, so he couldn't be sent home.

So, what should be done with dangerous Islamists you can't get rid of? Passports can be revoked, travel prohibited, for instance. Reporting obligations are another option. Islamists all over the country, among them certain Syrian refugees or released terror suspects, must respect these requirements already. A communication ban with certain people and mosques restrictions too might be imposed.

Nevertheless, even with all of these measures, there are no guarantee that potentially dangerous people can vanish from the radar. Full control will most likely remain an illusion. "There's always a residual risk," says a terrorism investigation veteran. "And sometimes the residual risk is named Anis Amri."