If Germany was able to prosecute SS guards from concentration camps after the war, why weren't they able to go after the SS officer who arrested Anne Frank even though they knew who he was and he admitted freely to it?

There was very little appetite after the war to prosecute in Germany by Germans. This only started lately..

As an example only very recently was 100+ year old camp guard prosecuted..

It also did not help that in many instances after the war these prosecutors were former nazis right up until the seventies