The martyr video identified the knifeman as Muhammad Riyad, the ISIS “soldier” who went berserk on Monday aboard a train in Bavaria, hacking and slashing at several passengers in the first ISIS attack Germany has ever seen. But that isn’t the name he gave to German authorities when he arrived last summer via Austria. His application for asylum bore the name Riaz Khan Ahmadzai, and nearly three days after German police cut short his rampage by shooting the attacker dead, his real identity remains a mystery.

During a press conference on Wednesday in Berlin, Germany’s top police official conceded that investigators are not sure about his real name, his age or even his nationality. Without providing any verifiable information about himself, the attacker was not just able to enter the country last summer – he was also granted temporary asylum status, housing, welfare benefits and, in the two weeks before the attack, he was assigned to a German foster family, said Interior Minister Thomas de Maizière. Only after he was shot and killed by police did investigators begin checking on his identity in earnest.

Authorities have discovered that he could be from Afghanistan or Pakistan, and that the information he provided to officials in Germany could be partly or entirely false. “Naturally it is often the case that the authorities have to rely on the information provided by the person concerned, especially when there is no passport available,” said de Maizière.

When it comes to refugees, that information is often impossible to check. Last year, more than a million asylum seekers came to Germany from across the Middle East and North Africa, and more than three-quarters of them crossed the border with no passports or other forms of identification, according to government statistics. Monday’s attack, which left five people gravely injured in the Bavarian town of Würzburg, has shown how little Germany really knows about the refugees it is sheltering. In many cases, the government appears to have simply given them the benefit of the doubt – a policy that has long worried conservative German politicians and security experts.

“You have to know who is in your country,” the center-right lawmaker Hans-Peter Friedrich, who preceded de Maizière as Interior Minister, told TIME last fall, soon after asylum seekers were implicated in the November terrorist attacks in Paris. “At the moment you have the opposite situation,” he said at the time. “You do not know anything. You do not know who’s coming.”

In the last few months, Chancellor Angela Merkel and other European leaders have moved to regulate the influx. The open borders that migrants used last year to reach Western Europe have been closed and, under a deal agreed with Turkey in March, the European Union has started sending back migrants who arrive from the Turkish coast. These measures appear to be working. Last month, only about 1,500 asylum seekers reached the E.U. by boat from Turkey, compared to more than 31,000 arrivals in June of last year, according to the latest U.N. data.

By easing the pressure on the German asylum system, this decline should help the government process the roughly 440,000 asylum applications it received last year, mostly from refugees fleeing the war zones in Syria, Iraq and Afghanistan. But it will not necessarily help the authorities verify the newcomers’ identities. As de Maizière noted on Wednesday, Afghanistan does not even keep records on its citizens that Germany could use to check against the information they provide. “There is no reference data from the Afghan registration bureau or anything like that,” he said.

Complicating matters further is the fact that at least 60,000 of Germany’s asylum seekers are minors who arrived with no parents or guardians. The Würzburg attacker was initially thought to be one of them, as he claimed to be 17 years old in his application for asylum. German authorities are now working to establish whether that information was accurate.

But so far, they have not announced any additional identity checks for migrants who arrived without passports. At Wednesday’s press conference, de Maizière urged the country’s social workers and volunteer groups to continue helping refugees from the Muslim world feel welcome in German society. That approach has so far helped Germany avoid the devastating Islamist attacks that have struck in neighboring France and Belgium over the past year. As the minister put it, “Good integration policy is good security policy.” Even when the state isn’t sure whom exactly it is integrating.

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