Often, greed is a central theme in malevolent true stories. Greed can drive people to act in extremely malevolent ways, such as embezzling funds from charities or defrauding the elderly out of their life savings. It's a sad reality that these things happen in the real world and they often make for disturbing but true stories.
Not all of them. There could be friendly ghosts in the stories. For instance, a ghost that protects a place or a family. It might be the spirit of a former owner who still cares about the property and its inhabitants. However, there are also likely to be malevolent ones that create fear and chaos.
Another theme could be the blurring of the lines between the living and the dead. In many first malevolent ghost stories, the ghosts can interact with the living world in a way that is both scary and mysterious. They might appear suddenly, or cause strange things to happen around the living. For example, objects moving on their own or strange noises being heard. This shows that the boundary between the two realms is not as clear as we might think, and it adds to the fear factor.
Well, one of the early malevolent ghost stories might be related to the idea of a banshee in Irish folklore. The banshee is a female spirit whose wailing is said to be a sign of impending death in a family. It's a very spooky concept. People believe that if you hear her cry, someone in your family will die soon, and she was often seen as a malevolent presence, bringing fear and dread.