But in order to frame him in the way that was shown to have occurred, they'd have had to have somehow found the woman's remains from the crime, which would have either been dismembered, or they'd have to dismember then themselves, and then burn them at Avery's salvage yard.
Which kind of means that, yes, they would have had to murder her themselves, or else basically the entire police department and every single person including folks like coroners would have to be in on it, because they would have had to find her remains wherever they were first located, recover them, transport them to Avery's salvage yard and burn them there, to later recover them there... And somehow no one knew about the body when they first recovered it? Or I guess it just happened to be burnt in Avery's salvage yard, in a fire that they know Avery started himself? The idea that was presented, that the cops were somehow framing him to avoid paying for the previous wrongful conviction, just didn't really make sense, because it would either involve the aforementioned recovery and transport of the victim's body to Avery's place, or just a totally coincidental murder of somehow on Avery's property.
Of course, he actually did present other evidence that was even more damning, like apparently non blood based evidence found inside the rav4's trunk from Avery, which couldn't really be explained even if you believed the notion of planting blood on the scene.
And then there were various things which are presented in the movie that really don't reflect reality, like the idea that the key just magically appears. It didn't, it has hidden on a small ledge behind a cabinet and feel to the ground when they moved the cabinet. It didn't just appear or something.
Like I said, you can look into it yourself, but I'd be really wary of basing an opinion on a movie that really isn't even a documentary. I mean, they actually denied the prosecutor an interview, and refused to even talk to him. That's kind of absurd if you are trying to do a serious documentary.
Here is an article taking about some of the evidence, but not nearly all of it, which was presented at the trial but is conveniently left out of the movie. Again, it's just a movie. It's made for entertainment.