It looks like it is clarified that it is RDM if you kill a victim of a failed kidnapping. It makes plenty of sense and it feels it should have been that way all along.
Tass could have been more generous with the rule being unwritten and such. He might have felt you didn't have the purest intentions and didn't want to extend the courtesy is what I am assuming.
I have been upset with gray areas and unwritten rules but I will have to disagree with having every rule written down. It is actually quite rare to see anymore than 1 page of rules for any DarkRP server and it is quite counter productive.
And I mean that the average age for anyone who players on DarkRP doesn't want to come home and study for another 10-20 minutes just to make sure they don't break the rules. God forbid that I am actually required to tell someone that they need to read a 7-8 page google doc and hold them accountable if they don't.