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
I knew a guy who got imprisoned for murder, really nice guy, the way he described it was an armed robbery where the armed person got spooked and fired off a shot. They were arrested on the road while taking the victim to the hospital (they weren’t trying to hurt anyone) and ended up getting booked for murder and kidnapping.
I met him a few years after he got out on probation.
Edit: fixed a typo