As the accused: get advice before questioning, admit nothing prematurely.
Anyone accused of fraud should seek legal advice before the first questioning. Under § 146 StGB, fraud requires an intent to obtain an unlawful enrichment and a deception. Whether these conditions are met is often a question of the individual case, especially with deals that have failed commercially. From a legal perspective, it is crucial not to make a statement on the matter without knowing the file.
You have the right to remain silent and the right to a defence lawyer. A spontaneous explanation intended to exonerate you can unintentionally become incriminating. First have access to the file taken and the evidence examined.