"What steps do the police usually take before a public search?
The public prosecutor and the police are obliged to examine and, if necessary, use milder means (measures that interfere less with the rights of those affected) to identify or localize unknown suspects or witnesses before initiating the public search. Since it strongly interferes with the personal rights of the wanted person, it is rarely the first step. First measures are, for example, the evaluation of existing traces, interviews with witnesses, police investigations or searches in the police information systems. A public manhunt, which is limited to a specific group of people, also precedes a general public manhunt, provided that it is promising in the specific case constellation. Only when these measures remain unsuccessful or do not promise any success in the foreseeable future, the police turn to the general public. The police measures are based on the applicable legal framework and are subject to the principle of proportionality.
In principle, the court is responsible for ordering the public search. Only in the case of imminent danger can the public prosecutor or its investigators initiate the public search immediately.
BKA - Öffentlichkeitsfahndung
This discussion leads to nothing, as long as it is based on the assumtion of the prosecutors behavior. If they had nothing in their hands, not a single german court/judge would permit the public inquiry. I wrote about that before. The step that the BKA (not the Braunschweig prosecuters!) did, demand reservation of a judge.
So we could likely discuss, if a court will give permission to an investigative operation that interferes so strongly with the rights of CB, without prosecutors who put their very promising cards on it's table before.
The answer is no, because german courts are pretty reluctant in that matter. The small amount of public inquiries in relation to prelimimary investigations in germany proves this pretty easy.
So as a result: If the prosecuters (BKA + HCW) had nothing tangible against CB, no judge would have admitted the BKA appeal. And that is no assumption but a legal fact!
Silence on the evidence doesn't mean nonenxistence of evidence...