the word murder, which means something, is a legal term
the concept of murder, however, is a much broader concept -- the unjustified taking of a human life and that probably has been around as long as humans have had a civilization...i think that in order for justice to exist, we need a civilization, which means laws, courts, culture, etc...
and it fits in with your BS -- because you believe that an all-loving creator g_d created everything perfectly, yet humanity right now isn't perfect (murders, rapes, etc), there has to be an explanation for that, making it humanity's fault, some inner taint of theirs...because your g_d would never create such a beast
except, of course, the times in the bibble where g_d commands and gives the ok for people to murder, rape, abuse & kill each other
and since your g_d doesn't change, is the same now as then, i'd be very, very concerned...i know where you put all your marbles -- in with a traitor to the human race...instead of with the imperfect, struggling, species that you belong to...but that's what happens when one takes things like g_d, moses, cain, the serpent literally...or something like that...