Masoud Aqil, a 24-year-old Kurdish Syrian journalist, has warned that German authorities need to be more careful about vetting people before they let them into the country.
Aqil makes the claims in a book titled “In among us: how I escaped torture in Syria only for it to catch up with me here", which is set to inflame a raw point in German political discussion.
In the book, the 24-year-old recounts how he survived sixth months in Isis captivity in Syria. During this time he says he was was tortured and humiliated, and regularly dragged from one jail to the next. In September 2015 he was freed in a prisoner exchange.
He now lives with his mother in Germany - just one of several hundred thousand Syrians who have been offered asylum or subsidiary protection in Germany since September 2015.
But he claims that undesirable people have also come into the country with him.
Some of them claim on social media that they want to carry out violence against “infidels”, or boast of brutal atrocities they carried out in Syria, the bespeckled Aqil says.
Others put pictures of Isis flags on their Facebook profiles while giving their location as in Germany.
“They aren't exactly the smartest people around,” he says.
Masoud Aqil at his book launch in Berlin in August. Photo: DPA.
Aqil advises the German authorities to look carefully into the identity of every asylum seeker, while cautioning that they should not throw the blanket of general suspicion on all asylum seekers.
But he argues that suspicions are always justified when someone arrives in the country without identification papers. The excuse that identification was lost during the journey could be true in some cases, he says, but adds that more often than not it is an attempt to hide one's true identity, often with the aim of swaying the asylum process in one's favour.
Debate has simmered in Germany for almost two years about whether Chancellor Angela Merkel's decision to open the country's borders to refugees in September 2015 led to a heightened terror threat.
The government long denied that potential terrorists were using the refugee routes to enter Germany.
But several terror attacks in the intervening period in which asylum seekers have been implicated forced the government onto the back foot, with critics insisting that refugees should not be allowed into the country if they do not have the necessary paperwork.
The most recent report by the Interior Ministry on extremism, meanwhile, claims that the number of Islamists potentially willing to carry out a terror attack in Germany has reached an all time high of 680 people.
But Aqil insists he has no truck for Germans who place all refugees under general suspicion.
In his book he describes a visit to a German doctor a few days after a Tunisian man drove a truck into a crowd of people at a Berlin Christmas market last year, killing 11 people.
On finding out he was Syrian, the doctor asked him whether he could drive a truck, to which he replied that he could.
“Then take a truck and drive it into an area full of people,” he remembers the doctor cynically telling him.