I was the ninja who attacked Rize. Here's my side of the story.
Me and the other ninja were trying to sneak from the cargo desk to the kitchen because the technomancer said they'd meet us there. We tried to rush past the medbay into the maintenance area below the living quarter elevator and were spotted by Rize, a janitor, and someone else. I would've just kept running for maint and hoped they didn't get a good look at us, but the room we were going to rush through had just been mopped and I slipped right in front of them.
Precisely because I didn't want to "speedrun my way to full armory distribution", I tried to threaten Rize and the two other people that saw me not to tell anyone that they saw us there. Shortly after we left, Rize reported us to the rest of security and the armory was summarily opened and the alert level was quickly raised to blue and then red.
A while later, I looked at a suit sensors console to see where Rize was and went to the security lobby to go after them. By that point, the armory was already opened, I think we were already on code red, Rize had heavy armor and a burst rifle, and the last time I saw the other antags they were in the bar surrounded by about four security officers with armory gear, so I thought they were about to get arrested. When I reached Rize, I was about to yell at them when they reported my location on the security channel, again, right in front of me. That's when I attacked them.
Maybe I could've just not followed through on my threat to go after them if they told people they saw us, but I think part of the reason that threatening people not to call security doesn't seem to work a lot of the time is because people think most antags won't go through with it.
I wasn't "RDMing" and I wasn't out to "decapitate as many security officers as I can". I was trying to kill Rize because I told them "don't report us or i'll shoot you", and they did it, twice, including once right in front of me.
That's on whichever players did that. It's not Kyres' fault what other players besides himself say.