This probably has its roots in the past, with Nazi lynchings were justice was just skipped and people thought they had to carry out a sentence themselves.
Although I understand the emotional conflict that arises from situations like these, it gives me actually confidence in the justice system of the nation I currently live in: if they even defend the rights of a murderer, this indicates they will also take the privacy of everybody else seriously.
Edit: I also don’t feel I need to know whether e.g. my neighbour served a prison sentence — the goal of german prisons is rehabilitation and they are actually not bad at that.