Just to clarify a few things: my two adult cats (the mother and the baby-eater) are sisters. I had planned to have them both spayed a few months ago but the baby-eater was very unwell at the time, so I decided to postpone the spaying for both of them so that I could eventually get them both done at the same time. By the time the unwell cat had recovered the other had already snuck out of the house and fallen pregnant, so I resigned myself to letting her have the kittens and then taking them both to be fixed. That's how this situation happened. To those questioning whether I was aware of the potential danger, yes I was, but the mother cat is usually dominant to her sister and intimidates her a lot, so I assumed she'd chase her away if she tried to go near the newborns. Instead she seemed indifferent to the situation and simply stood by while her sister killed the litter. As for why I did not intervene, I was not in the room at the time. I entered the room and saw the cat had given birth, then exited the room to go and fetch her some extra food and water. When I returned I found the sister in the room with blood around her mouth, half a leg on the floor, and the mother sitting off to one side washing herself. As I stared at the scene in a mixture of surprise and revulsion, the killer began coughing violently then vomited. So that's how you came to read about this event. As for those suggesting I should punish the killer in some way, I am not going to. She was just acting on instinct, like all non-human animals do. And I think that's all I have to say for now. Sorry for the long comment.