It’s well documented that serial killers tend to preferentially go after the homeless, drifters, addicts, sex workers, etc because they know the law gives no shits about them and will probably not even bother to investigate beyond a superficial glance let alone actually prosecute. Those groups are effectively medieval-style outlaws that anyone can kill if they wanted to. You’ll even get police flat out saying that investigating their deaths would be “more trouble than it’s worth” or “divert resources from more pressing matters.” They’re literally viewed as subhuman in the eyes of the law.