Is it in principle valid to extend to concept of murder beyond just humans?
Certainly there are penalties for killing animals under certain circumstances, although our whole carnivorous culture is fraught with so much paradox there, you need to start differentiating between morals and ethics to make any sense of it. Or to put it more simply, it's OK to kill a cow but not a dog depending on what country you're in (or the other way around), or it's ok to kill to eat it, but not just because you don't want to take care of it any more, or just for sport (e.g. cock fighting or bull fights).
But whatever the circumstances with animals, our legal system does not consider that equivalent in any way to killing a human being. You are not going to be executed for killing a dog or a cow, but you could for killing another human.
The scope of this question goes way beyond the animal species we have on this planet. If we created an artificially intelligent, human-like mind - would it be murder to destroy that? If we discovered a tribe of neanderthals living peacefully somewhere (just a thought experiment), and then some human went and shot one of them dead just for sport - would we consider that murder? What about a half-breed neanderthal/human? What about an alien species we discover on the planet mars? Dolphins?
How far away from the human genetic tree do you need to get before it's no longer murder with the same penalties we hand out for murdering humans?