I think this story begins and ends with Manitowoc Co. law enforcement. To me, it doesn't make sense that some civilian killed her and then they got involved in the coverup by planting evidence. Like how would that work? Did the cops approach an outside person about taking Halbach out? I can't see that happening.
Another possible scenario (but a bit of a stretch) is that they just lucked up and had a missing woman that happened to have last been seen at the Avery salvage yard, was killed and then they decided to take it from there. Maybe they found Teresa's body somewhere else and then hatched a plan to frame Avery. I honestly can't see this happening. What are the odds?
I think Avery was under surveillance at almost all times. The county had to have known of the impending 36 million dollar lawsuit--those just don't pop up out of the clear blue one day. So the goal of the Sherrif was to catch him in any type of situation where they could move to get him outta the picture AND taint his name.
36 million dollars would bankrupt that backwoods county, thus destroying the lives of all reaches of the justice system involved in the initial rape coverup (officers, judges, lawyers, etc.). They simply weren't having it and they decided that Avery wasn't going to take them down after all they'd done to put him away the first time. At this point, the gloves are off and all options are a possibility.
Halbach walked into a perfect scenario for the cops, unfortunately. Officers could've easily gained access to her after she left Avery's house by pulling her over. And this could've easily been done without anyone seeing as the area is very rural. They take her out, stage the RAV4 with Avery's blood and put it in their salvage yard. Same with the bone fragments. They staged everything they initially could and then planted the rest after gaining access to Avery's home.
Think about it--NOBODY would dare question cops. So there's no worries about a crime scene being discovered. There's no worry about scrubbing all traces of evidence because it could be in plain view and nobody would think to swab a cop car for DNA or something like that. Why would anyone accuse a cop when you have this outcast Avery already being fingered as the suspect? They went right to his salvage yard, making him a suspect from the jump. They knew exactly what they were doing.
I don't think that ALL law enforcement was involved in this. But if you think about the key players--Lenk and Coburn--they had risen to higher rankings in the unit. They knew they could use that power to get their underlings to unknowingly help them accomplish their task. They used the unwritten police code of deferring to senior officers to push their narrative of what happened AND gain access to the Avery property in order to help physically craft that story.
I'm rambling now, but I have a million more thoughts about this damn case.
I may have to watch it again.....