The men, aged between 27 and 51, will stand trial on charges of membership in a foreign terror organization and of supporting a foreign terror organization.
Prosecutors claim that the figurehead of the group was 33-year-old Iraqi Ahmad Abdulaziz Abdullah A., known to associates as Abu Walaa.
They describe Abu Walaa as Isis' “ambassador” in Germany and claim he had direct contact to the group's leadership.
According to the charges, Abu Walaa built up a super-regional recruitment network based around his mosque in the small town of Hildesheim in Lower Saxony.
According Die Zeit, Abu Walaa travelled the length and breadth of Germany giving radical sermons, and had contact with Anis Amri, the Tunisian man who drove a truck into a crowded Berlin Christmas market in December, killing 12 people.
The others accused are Turkish citizen Hasan C., German-Serbian citizen Boban S., German citizen Mahmoud O., and Cameroonian Ahmed F. Y.
The men were arrested in November 2016 after months of police investigation in North Rhine-Westphalia and Lower Saxony, and have been in detention ever since.
The charge sheet lists eight concrete occasions on which fighters were sent by the group from Germany to the Middle East in 2014 and 2015. Among these recruits were Mark and Kevin K., twins who blew themselves up in suicide attacks on the Iraqi army.
The charges are partly based on testimony provided by “confidential persons”, who had once been in close contact with Abu Walaa. But he had come to see them as traitors and called for their murder, according to Die Zeit.