After I watched this episode, which was very good, I started reading blogs and reading little things family members had said, and I'm almost 100% certain these women were killed by Drug Dealers. There is no Serial Killer. There is no Rogue Cop. It was probably a ruthless Mexican Cartel that wanted to send a message "Don't Mess with Us." Lots of people knew these women were dead and were buried on the West Mesa. Somebody wanted them to know. If it were a Serial Killer, probably nobody would of known. However, many people seemed know there were women getting killed and being buried there, including some women that died. Probably, Drug Dealers spread the rumors.
Also, trying to blackmail the family, would be something Drug Dealers would do. Cutting off breasts and stuff like that is what Mexican Cartels do. Yes, serial killers do this to but it's sort of drug cartels calling card. They want to people to know they mean business and that they are there. Also, these women were killed by more than one person.
Now saying it is Serial Killer helps scare women off the streets and lets cops off the hook, because one of the suspects who probably was a Serial Killer died around the time the killing stopped. It's also more salacious. Saying a Cop killed the women is just a way to hurt the cops because people don't like cops. But this is pretty obvious.