Do you think hitmen really exist?

I am making reference to the way they are depicted in movies and video games take into account John Wick/Agent 47 the guns blazing and action bit might be stretched beyond reality but.....how scary is it to think someone could drop like a stone on the side walk from a sniper and no one may ever know who did it? how many people fall ill to food poisoning and maybe the food was poisoned on purpose....how many people have had a "heart attack" mysteriously with no known previous issues or health complications.......how many people that are found strangled beaten shot in general may have had their life traded for $$$ or drugs? do you think your neighbour could be a cold calculated professional killer?