I believe Steven Avery is guilty but I also believe that there's not enough evidence against Dassey and that Dassey should not have been convicted.
I don't think the prosecutors have a good explanation of exactly how the murder happened and their attempts to try and prove that it happened in the garage don't fit the evidence IMO.
That being said, it's been proven that Steven Avery lied about not meeting up with Halbach, and his phone records and prior behavior around her strongly suggest he was targeting her. When someone goes missing and their car is found on the property of the last location she was seen alive, that's pretty strong evidence that somebody on that property had something to do with her disappearance.
I don't believe in Zellner's mass conspiracy theories. I see some sloppy detective work perhaps, but not an organized conspiracy.
Furthermore, Zellner's credibility is shot when she tried to claim that Steven Avery's vacutainer blood tube had been tampered with by pointing out that there was a hole in the rubber stopper.
Anybody who has ever drawn blood before knows that there's SUPPOSED to be a hole in the rubber stopper where the tubing penetrates into the EDTA tube. The fact that she didn't bother to ask a real phlebotomist or medical professional about this proves to me she had a conclusion beforehand and was in search of evidence to prove her theory.