Depends on the translation.
Most modern translations use "murder" instead of "kill". Murder, which is the English word for "wrongful/unjustified killing", is a better translation of the Hebrew, considering how many places there are later in the same book where God orders the Israelites to kill people (Canaanites, idol-worshippers, people who work on Saturday, and murderers, among many others). We still make distinctions like that today. Killing in war, in self-defense, as official legal punishment, as euthanasia -- most people believe that at least some of those categories are at least sometimes not murder, even though the tragedy of death is still just as present.