I've long been of the opinion that people who claim that only a belief in god prevents them from killing someone haven't really stopped to think about that claim. Belief in god just isn't sufficient, there's something else at play (we "evolutionists" call it empathy). Your own bible confirms this. Way back in Genesis, you have the story of Cain and Abel. Now Cain knew with 100% certainty that god existed. He actually spoke to the being and heard back from him. This is evidence (in the story, at least), beyond anything current theists can muster.
So, Cain knew for a fact god existed, knew that god considered murder wrong, and still was able to kill his brother. The belief in god didn't matter.
Now, you can argue that at this point, there were no Ten Commandments, and that murder hadn't been invented yet, let alone declared a sin, so let's go forward in time to King David. David was born after the Ten Commandments were published (supposedly), knew murder and adultery were sins, knew that god existed (again, through direct contact), and he was still able to cheat on his wife, sleep with another man's wife, and then have that man murdered to cover up the fact that he got her pregnant!
So, I'm sorry, but belief in god doesn't seem to matter when it comes to preventing people from committing murder (or various other anti-social behaviors).