How did Johan get away with this?

So, we know that in Munich many kids were playing the rooftop games. Johan is always seen walking around w/ many kids. In ep 33, Dieter also talked to one of the kids that was involved in it and knew Johan and mentioned that he couldn't become like Johan. Why didnt Dr Gillen and Reichwein use one of the kids to admit about Johan being involved?? Dieter told them about how one of the kids said that Johan said he was gonna get killed by a Japanese man. So, like why didnt Gillen and Reichwein use their testimony as a way to question him and prolly prove Tenmas innocence in the process.

So, we know that in Munich many kids were playing the rooftop games. Johan is always seen walking around w/ many kids. In ep 33, Dieter also talked to one of the kids that was involved in it and knew Johan and mentioned that he couldn't become like Johan. Why didnt Dr Gillen and Reichwein use one of the kids to admit about Johan being involved?? Dieter told them about how one of the kids said that Johan said he was gonna get killed by a Japanese man. So, like why didnt Gillen and Reichwein use their testimony as a way to question him and prolly prove Tenmas innocence in the process.