First things first:
when you told him to go to the tester were you a Detective? Because if not you can't force him to test nor call a KOS on him for not doing so and he had every right to kill you for false KOSing him.
Second of all:
if you want anything to happen against staff members (for example because of breaking rules) you will have to file an
Abuse Report here with
sufficient evidence e.g. screenshots of logs or a video showing the situation. Also use the template that Henny provided, just click the edit button on your original post, paste the template in and fill it out.
I'll move this topic to the appropriate section for you.