<color=red>The Mundane Killer? For reasons being that when the police find the bodies, there is no significant calling card. The killings may be barbaric, but, it could related to other things. Gang violence or just random murders.
It could be anybody. Ruling out medical experience, means that the murders looked rushed. Or amateurish. It's in L.A., so, there has to be some sort of air of hostility. Most movies based in L.A. have either a steady threat of gangbangers, homeless, junkie, or insane people present.
Not to mention the disgruntled employees and vigilantes. A killer who kills in a city rich with suspects. He plays it safe, he doesn't detract from his way of killing. He probably doesn't murder frequently or kill the same kind of people twice. He's textbook insane.
He is <color=red>The Mundane Killer.