Not just uncaught murderers, there are a lot of people who have killed without legally being considered murderers.
People who killed people in accidents such as driving accidents or hunting accidents
People who killed in self defense
Soldiers who killed enemy soldiers
Executioners
Police officers who have killed on duty
Doctors and nurses who have made mistakes that accidentally killed patients
You are not responsible. Even if you argued with someone, you couldn’t have known what the outcome would be. Heart attack or they spent a bunch of time pissed and got in a fistfight later that resulted in someone’s death. You cannot control what they choose to do as long as your actions weren’t intentionally leading the other person to make those choices.