Actually that is one of the biggest and most misinterpreted of the commandements. It states, "thou shalt not murder." There are plaenty of justifiable reasons to kill and the Original scriptures were aware of those.
OVER 2800 YEARS AGO BEFORE GUNPOWDER WAS EVEN INVENTED THERE WAS THING CALLED; THE 6TH COMMANDMENT THAT SAID THOU SHALT NOT KILL YOU SEE, IT'S A PEOPLE PROBLEM, NOT A GUN PROBLEM