A writer should have a variety of interests.
Reading and writing are amongst the top endeavors but writers need to be masters at mood, characterization, and world building. With autumn here and Halloween a few days away, paranormal reality shows top the list of how to build suspense, intrigue, and horror.
A recent episode of a ghost hunting show explored the house of a serial killer. Not their first exploration, but it still gives a writer insight into what a depraved mind thinks like and does.
Normal people do not have these inclinations. We simply go to a movie. So being able to witness the supernatural underpinnings of a lunatic helps grease the wheels in the inner mind of a writer.
Poison people. Bury them in the yard... I have always joked that I would bury people in their yard, but I have a sick sense of humor.
Practicality aside, serial killers have a vanity complex. They must own what they kill. Almost like cannibals who eat their victims must own the spirit, soul, and energy of the person they have conquered.
So as you write your horror fiction or poetry, remember to understand that killer and the victims in your made up case. You never know what haunting evidence will lead your reader to read your story again and again.