Here is a different question - what makes it an atrocity? You could be technically correct and say "Because other people decided it." but that doesn't give any insight into why.

A natural rights framework has the thumbprint of a lawyer along with outmodedly telological way of thinking that can only see a wrong as a "crime" but is willing to construct justifications for what they already believe.

But mixed in the principles isn't just accepting "is wrong because I said so" as a proof. Thus it has contrived post hoc cruft to achieve consistency with assumptions but also underlying ethical principles.

You just admitted that it was an atrocity however. That implies the people who were killed had their rights violated. Your concept of rights granted by the government to the people is not self-consistent.

That's not a definition of atrocity that I'm familiar with. We could extend this to quibble about the definitions of evil, cruel, what have you, as well, but it's a wide diversion at this point. "Nature does not guarantee you anything" is not "there is no such thing as moral right or wrong."

Let's ask a different question: if there are inalienable rights, what is the complete set? Do you expect everyone to agree on what that set of rights is? If one person doesn't believe that guns are one of those, and another does, how do you break that tie? If there is truly a certain set of rights that's a law of nature, should everyone converge on the same set?

My point is that it is virtually impossible to establish the concept of wrongdoing without the notion of certain innate rights having been violated.

Each person has their belief of what they hold to be human rights. As human beings, it is the duty of each of us to protect what we respectively believe to be the rights of our fellow human beings.