His fingers fly across the keyboard, and his hard drive is full of information on possible terrorists from the self-styled Islamic State. Masoud Aqil is looking for screenshots he took off Facebook profiles after a suspected IS supporter wrote very openly to him about his radical views after arriving in Europe.

The man, whom Masoud remembered from Syria, no longer has a Facebook profile. "It is hard to believe how open many of them there were in the beginning," the 24-year-old told DW. It was in early 2016, when Masoud, a Kurd who fled to Germany via the Balkan route, suddenly realized that IS - his cruel torturer - was also in Europe.

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Masoud was held captive in six different IS prisons in Syria between 2014 and 2015. He and his colleague Farhad were kidnapped by the group at a street crossing while they were on their way to an interview. It was December 15, 2014, and the Syrian intersection was not controlled by IS but by the Kurdish People's Protection Units (YPG). They were far outside the area that their group controlled when they seized the two men in Rojava in Northwest Syria.

Did IS get a tip?

There is a lot to suggest IS received a tip that the Kurdish TV journalists would be passing through. Masoud and his partner Farhad Hamo were not entirely unknown by then. For 20 months, the two had filed almost daily reports from the field for their TV station; reports on political and social themes as well as the way the war was developing.

The Kurdish leadership in Rojava was in the process of stabilizing the area and establishing its reputation as the most important adversary of IS and as the only party in the Syrian conflict receiving help from outside the country: from the Kurdistan Workers' Party (PKK) in neighboring Turkey.

Read more: The Middle East's complex Kurdish landscape

Turkish Kurds are widely believed to have been the first to supply their Syrian brothers with arms. Today, Rojava's YPG fighters are part of the US-led Western anti-terror alliance. Their knowledge of IS is worth its weight in gold.

The Islamists, says Masoud, desperately sought support from those people left behind: "People who were living in most of the IS areas were living in the desert with no schools. The Syrian government was just ignoring them. So they were trapped there with no livelihood. So these kinds of people were open to radical thoughts, too. IS knew that and targeted them, they were successful in exploiting that."

That was the backdrop against which the young video journalist and his partner were kidnapped and thrown into the IS torture chambers. It was an ordeal much like martyrdom: "They questioned me while they tortured me. They beat my legs and my back. They hit me in the face, pulled my hair and screamed at me - calling me a Kurdish infidel and telling me that all of the Kurds should be killed. All of us - because we were keeping the region from becoming Islamic in the way the Islamists wanted it."

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Masoud's experience says a lot about the way that IS leaders think. Many of them were recruited from the ranks of the disbanded elites of the Baath party in neighboring Iraq. When he arrived at the second prison in Syrian Al-Shaddadi an admission form was filled out - as if they had actually become some sort of state: "It's like a prisoner ID in the IS prison. And the papers were filled out by an IS member from Tunisia."

Chatty IS fighters

The henchmen also made mistakes: "They sent IS informants to me to prove the power of their organization," explained Masoud. "They showed me newspaper articles and videos from Western media outlets reporting on the growing threat posed by IS. They were proud."

Too proud, perhaps as Masoud says. Since they seemed to think they were going to die anyhow, the IS informants that came to his cell and spoke openly about murders that they had committed. They shared details that the young Kurd still remembers very well today. "One of my sources of information was what I heard in prison. And IS members and civilians who knew other IS fighters. That information helped me find potential suspects and terrorists who later fled to Germany in 2015 and 2016."

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Masoud survived 280 days in the torture chambers. When he was released in a prisoner exchange, he immediately fled to Germany.

Passing information to German authorities

And when he came, he brought very precise information with him. So precise, that experts like psychological therapist Jan Kizilhan consider his reports to be highly credible. Kizilhan is a professor at the Baden-Württemberg Cooperative State University and has also been tasked by the Stuttgart state government with looking after Kurdish Yazidi women who spent time in IS prisons and are now living in southwest Germany.

Masoud's ordeal seems to have sharpened his memory, for he has written protocols with the names of a great number of terrorists and IS supporters. In a new book written with Berlin journalist Peter Köpf, which will be on bookshelves in late August, Masoud Aqil explains why he is not hiding his identity and why he is standing up to IS: "I don't want these monsters to establish a state in which the laws of the jungle apply in Germany, so I decided to turn over everything I know - all of my information - to German authorities."

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That information is indeed helping Germany's police in ongoing investigations today. Although the Federal Criminal Police Office does not talk about individual cases, it is obvious that they are taking tips from refugees much more seriously. Masoud Aqil says he still sometimes wonders "why I wasn't really questioned when I got here." Apparently German authorities were slow to recognize just how important information gathered from the hundreds of thousands of Syrian refugees who arrived in Germany via the Balkan route in 2015 could be.