no the law had to exist before we could punish a person for doing it,,, the unlawful part of the definition is a modern addition,, go back far enough and you wont find it,,
you cant make a law against something that doesnt exist,,
you said hitler didnt murder jews because you didnt know what the laws were there,, but you have shown how murder was determined centuries before hitler even existed,, so that should show you that murdere existed but they just didnt have laws against doing it to jews,,,