I don't think that that's what happened. The newspiece states quite clearly that the suspects were kept in jail as a preventative measure, in complete accordance with Germany's regional law.
The controversial part was that arguably the length of the preventive jail stay contrasts with the jail terms that the suspects are facing, and other regional courts determined shorter preventive jail terms.
I think that this is an issue where the court had to draw a line in the sand within the boundaries specified by the law. The court had a group of people known for conducting criminal acts and determined that the likelihood that they would continue their criminal activity if they would be released was almost certain. The court had to make a call, and had to choose between being responsible for allowing criminals to repeat their crimes, or ensure they wouldn't by keeping them in preventive jail.