may be of use re killing blow bug

Am sure it's a bug of some sort now, as this person died without any more or other player playing a part. His corpse looked like this. The discolored flesh of Agacak's corpse rots and peels from the flesh beneath. That seems to suggest that it was my plague that finished him off, not the vault or the poison? Or could it be the poison? Either way, I don't get a killing blow message, so I am assuming that I am not getting any credit for the kill either?