On the other hand there is the equally villainous Russ McGowan, a Philadelphia police sargent. He doesn’t kill anyone. He doesn’t do anything illegal. He’s just a vicious man. He feels women have no place as police officers. He’s not much more tolerant of minorities. He believes that special interest groups and political correctness have catapulted women and minorities to detectives at the expense of white men. He wants only team plays in his squad; not anyone with a mind of his own. And, if things go wrong rather than support his detectives he’ll find one to blame for his failure. Fall on your sword or McGowan will stab you in the back. He’s a Teflon man. No failure sticks to him. He always has someone to blame. And get with the program or be transferred.
So who’s more of a villain? It’s obvious that Thomas Samuels, a serial killer, has become a pretty vile person. But McGowan leaves an equal amount of destruction in his path. Many of your have had bosses like McGowan (I know I have; he’s based on one). They crush those who don’t play by his rules. As bad as a serial killer? Maybe not, but pretty vile nevertheless. Who do you feel is more villainous — the decent man turned serial killer or a boss who cares only about his own advancement?
There can be more than one villain in a novel you write. There’s the one who commits the crime that your protagonist attempts to solve. But, why not add others deserving of the word though he/she may not have committed a crime (a landlord who refuses to make repairs, a security guard in a store who keeps his eyes peeled on a teenager or a person of color due to his own prejudices, the boss who makes your life hell). Populate your novel with a variety of characters . . . both good and bad. Your readers will be appreciative.