Sorry, but you are completely incorrect in this matter. White collar crime is prosecuted fiercly in Germany, especially when it's a case that got public attention. However it takes far longer than it would in the US, because prosecutors are extremely thorough to guarantee a conviction.

We have far less of an acceptance of plea bargains. Pre-trial deals are almost unheard of, because the defendent can "come clean" at any time of the trial and the timing must not enter the judgement to their detriment. OTOH a defendent also has nothing to gain from co-operating early beyond whatever he/she is absolutely required by law to do. This means that the prosecussion will almost always have to do the entire work of proving beyond any reasonable doubt that the accused is guilty. Which they have to do on paper long before the first hearing is held.

Hence, cases brought to trial in Germany are generally water-tight. Stadler is almost definitely going to prison. The only question is for how long and who else he implicates.