I imagined a black man in tribal costume (loin cloth and not much else) holding a small unidentified bone in his right hand and pointing it across vast distances at some poor victim. The bone pointer could not be brought to justice for this form of murder, because he could be far enough away that no-one could say for sure he had anything to do with it, even thought the whole tribe would know who the witch doctor was.
That was when I was a kid. Now I have other notions. I think curses work best if the one cursed knows about them. Heck, they can work even if they haven’t been cast. A silly woman whose son is a pal of mine is convinced that, because I’m a witch, her son and I have been putting hexes on her. As if! It’s not actually what modern witches do if they’ve got any sense. But this lady is very good at getting herself into trouble and blaming others. She never puts the responsibility where it belongs.
I do think angry or hostile thoughts create energy, mind you, so some people might feel the effects even if they don’t know anything specific about where the bad vibes are coming from. And guilt feelings can also play a part.