If "Thou shalt not kill" were the proper translation, no person who took the Ten Commandments seriously could kill in self defense, even if it meant loss of the threatened person’s life, or could kill in warfare, even if his or her country were attacked. There could be no capital punishment no matter how horrible a person’s crimes were. Clearly there are cases where the Torah permits the taking of a human life. And, if it is sometimes permissible to kill another person, most people would agree that there are circumstances when it is also permissible to kill an animal. Judaism does not consider that the sixth commandment refers to animals.
Since the sixth commandment has been so frequently mistranslated,
two prominent Jewish commentators, Rabbi Samuel ben Meir (Rashbam) and Rabbi Joseph Bekhor-Shor,
explained at great length that the Hebrew text refers only to unlawful killing.
Both scholars stressed the differences between the Hebrew words for killing and murdering.
So the common Jewish belief is that the sixth commandment should be translated as "Thou shalt not murder."