Nobody actually believes the cops killed Theresa Halbach. Avery doesn't and his defense team didn't and I don't think you could reasonably conclude from all of the information out there. But that doesn't mean the cops didn't try to pin the murder on him.
I think the easiest explanation is that someone murdered Halbach near Avery's property shortly after she took pictures of the van and decided to hide her vehicle in the salvage yard. When her disappearance was reported and the cops knew that Avery was the last person to see her alive, they assumed that Avery did it and went about making sure he was convicted, regardless of whether or not he was actually guilty.
I believe the simplest explanation is generally going to be the right one in these cases.
You are suggesting that a third party and the police, acting independently of one another and at different points in the timeline, both conspired to frame Steven Avery, who was completely uninvolved in the murder of this woman even though he was the only one who we know interacted with her on the day in question, and the only person living anywhere near where her remains were found that actually had a personal connection to her.
That, to me, is a stretch. To say the least.
What's more likely?
A vast conspiracy involving multiple parties acting independently?
Or that this one guy, who has an extremely low IQ, has a history of odd, violent, deviant behavior -- which very likely got much worse in prison because that's how prison works -- murdered this woman and then did a terrible job of attempting to cover up the evidence?
You're aware before this trial that he was on the verge of being awarded a massive amount of money for being the victim of the kind of multi-person conspiracy and frame-job you're saying is so unlikely right?
Absolutely right. Manitowoc County had already framed him once before. I'm not sure if he did it or not, personally. But Manitowoc County cops shouldn't have gone within 1000 yards of that crime scene. Considering his pending lawsuit against them, on top of the previous false conviction that was attained with CLEAR prejudice against him, there is no reasonable explanation for why Manitowoc County cops were ever there to begin with, much less to be the ones who found the "evidence" (On the Eighth search of his bedroom, mind you)
At the very least, Avery should be immediately released and given a new trial, one which excludes ALL evidence collected by Manitowoc County officers. He should have a trial where no one on the jury has any personal connections to Manitowoc County employees. That way if he's convicted, we can at least pretend it was fair, unlike the trial that put him away. That trial was just a sham on multiple levels.
I will say I'm extremely happy to see that Dassey got his conviction overturned. The entire series is disturbing, but the Most disturbing part of it all was watching those cops completely take advantage of a young kid with a very low IQ, forcing him to tell them hours worth of obvious lies under the pretense that "telling the truth will keep him out of trouble", and then using those statements to put him in jail for a long, long time. It was disgusting, frankly. I had a hard time watching it, and I'm glad to see that injustice undone.