I've spoken with Kessi about this situation and looked your report and what you've said in the comments. According to him, he had came up from the bottom of the tester and you were standing in the doorway directly over an unidentified body. As stated in Rule 2.6, ignoring unidentified bodies is a valid KOS reason, so Kessi was within his rights to kill you for this. You haven't given any evidence to contradict this, so this will be denied.
Whilst it's true that people shouldn't be killing just because you are in the vicinity of an unidentified body, instead only killing when you are actually ignoring the body, that doesn't appear to be the case here, as you were directly on top of it showing no intention to identify it.
Thanks for making the report, and if you want to be safe in future, I'd suggest recording your gameplay with some form of shadow play. If you have any other evidence regarding this situation that you would like to share, you can DM me on discord, found in my signature.
No action will be taken.