Hi I was the Staff member that approved and oversaw this PK, I want to say firstly thank you for using the forums to your ability and making this PK appeal.
To firstly start with the Kangaroo court aspect in roleplay members who attempt or end up in rigging courts is an IC issue and nothing beyond any use of power or metagame in those instances of them doing that can be punishable or reverted. The only case that something along that is breaking guidelines is if fabricated evidence is presented which was not mentioned whatsoever. On the topic of the Rule you brought up, I think the Context of it has confused you it states
The punishment must fit the crime and you cannot be sentenced to death for MINOR offenses, meaning that you cannot be sentenced to death for something small, 5 NSB officers made a testimony on you committing a class 4 felony 4 times. The judge had the judgment to sentence you to death for these crimes that you were found guilty of. At the end of the day, the verdict of the judge is his judgment in most cases and not directly off the lawbook. Meaning that just because you're case doesn't meet the classifications of the law book on what you were charged doesn't mean it doesn't fit the crime.