One of the most remarkable episodes of Todenhoefer's trip to the ISIS-controlled region came when he was able to conduct an interview with a German fighter who spoke on behalf of ISIS's leadership.
"Our expansion will be perpetual ... And the Europeans need to know that when we come, it will not be in a nice way. It will be with our weapons. And those who do not convert to Islam or pay the Islamic tax will be killed."
Todenhoefer asked the fighter about their treatment of other religions, especially Shia Muslims.
"What about the 150 million Shia, what if they refuse to convert?" Todenhoefer asked.
"150 million, 200 million or 500 million, it does not matter to us," the fighter answered. "We will kill them all."
The interview became testy when they reached the topic of beheadings and enslavement, especially of female captives.
"So do you seriously think that beheadings and enslavement actually signal progress for humanity?" Todenhoefer asked.
"Slavery absolutely signals progress," the man said. "Only ignorant people believe that there is no slavery among the Christians and the Jews. Of course there are woman who are forced into prostitution under the worst circumstances.
"I would say that slavery is a great help to us and we will continue to have slavery and beheadings, it is part of our religion ... many slaves have converted to Islam and have then been freed."