Unless I'm missing something, all I'm seeing here is a dead mob, and a guy leveling up. However, he is seem to be wearing a low level outfit for someone fighting CMs. Which is odd. I can't really tell with all the red words in the way.
Though the fact is: it going to be really hard to tell who 1hitKers are because of the rebirth system. There are a lot of overpowered characters now who are able to 1hitk some mobs.
Please try to capture undisputable evidence please.
Edit:
I know that sounds kind of hard, but I can't and won't ban people who didn't deserve it.
And yes, its possible. I receive PMs with screenies with undeniable evidence of hackers.
Anyway, thanks for reporting, its good to know we have some concerned players :D.