This goes much further into philosophy, politics, and legality than I'm comfortable with but there's lawful and unlawful killing, the difference being... well,

This goes much further into philosophy, politics, and legality than I'm comfortable with but there's lawful and unlawful killing, the difference being... well, one is allowed and the other isn't, as per the law (be it national or e.g. international / warfare laws). I can't even make a statement whether killing is always morally injustifiable or not.