Don't murder.

רָצַח is the verb, and it's more typically used of pre-meditated acts of killing someone, though it's range extends to manslaughter. It's general meaning also tends in the semantic range of 'unauthorised' killing. In my view, 'Don't kill' is undertranslating the term, and leads to misunderstandings that somehow the Decalogue in the Hebrew Bible forbids killing altogether, which even a brief read of context would tell you is incorrect (not least in that the death penalty could be applied to those who broke this commandment).