Why would you expect the murder rate to be constant? It's plausible the opposite is true that the more murders there are, the more publicity they get overall and the more cautious would-be murderers become.
they didn't expect it to be, they said if it remains constant.
You seem to be the one making the assumption -- that it wouldn't remain constant -- otherwise why would you have made that comment?
If I am making the wrong inference here then I put it down to the strong and yet imprecise language of "it has everything to do with it".