Not to discourage any further answers but these older threads might be able to settle it for you (though in history, nothing is ever "once and for all").

/u/Georgy_K_Zhukov on the origins of dueling in the Renaissance is a good place to begin.

This answer on murder in Rome by /u/toldinstone which touches on the illegality of carrying weapons within the city proper.

This answer by /u/XenophonTheAthenian investigates the role of law enforcement in ancient Rome.

On a more unhappy but related note, /u/arte_et_labore's answer on the legality of spousal murder in ancient Rome.