Where did this movie theme come from?

I absolutely love horror film music, especially the more spooky and chilling kind, and one of my favorite pieces is the uncomfortably chilling opening theme music for the 1980 film, The Shining, which I thought had been an original piece of music. However, I recently saw a corny low-budget movie, called Shriek of the Mutilated, which apparently came out several years before The Shining but had the same musical theme in the movie, though somewhat varied. I am a little put off, since I thought that this piece was an original piece for The Shining, but here it was, used in another movie, and an earlier one, at that. Might anyone know the actual origin of this piece? Was it originally a clical piece of something?