It's usual in germany to inform the suspect about the intention to charge for a particular crime. The suspect, or his/her solicitor if there is one, get's the possibility to comment on that in a particular timespan. Then the prosecutors decide, if they charge or don't.
Of course, every suspect will get a subpoena, before all of this. If a suspect is being under the support of a solicitor, the solicitor will always give the advice to remain silent, until he has granted access to the files, that build up the case.
So yes, CB should have gotten the "offer" of being interrogated. But FF should have replied, that his client will refer to his right to remain silent, until getting access to the files.
That's it.