In my view of things to say "yes" I would have to think that these people did not have quite a human nature, that is to say we cannot consider them human in the same sense that we consider other people human. And it is not through their actions that they have gained this label, indeed before they did anything wrong their very being caused this. To say yes I would have to say that these people, by virture of simply being who they were, were not worthy of being alive.
I am already having problems, I have trouble saying that about any human being.
Now you might say to me, "but MN, by allowing these people to kill others, you are implicitly saying that the killer is more valuble than the victim!" And it is not an easy objection to deal with. But the fact is, I never had any opportunity to help those victims except this one. And the opportunity I am given entails something I find morally reprehensible. I lament what happened to those victims, if I was really given this choice I would curse fate for not giving me any way to help them free from morally wrong. But ultimately I have a choice between an action I believe is morally wrong, and an inaction that will bring about tragic consequences. I choose the inaction, I am not a consequentialist.
I know that sounds heartless, but one of the rules I live by is "do nothing contrary to human dignity" and by which I mean "do not deny the personhood of a human being." I cannot violate it. But inaction is a different manner. Though it is a bad thing to allow another to suffer through inaction, it is not as reprehensible as denying a human's personhood, at least in my view of things. As a clarification I mean that instead of saying "it is wrong to allow another to suffer through inaction", it should be said "if it is possible to take help someone out through a reasoned, moral action, then to allow them to continue to suffer is immoral."
So, no I would not kill them.