No. Again, the DNA was not 'found from sweat'. That's just what the prosecution argued. It was simply DNA, likely from skin cells. That's all that was known. And the technician who took the sample testified on the stand that he/she did not change gloves after processing other evidence that had Avery's DNA on it. So it's entirely possible that DNA was transferred onto the hood latch by the technician. It wasn't considered big evidence at the trial, from everything I can tell.
Brendan said a lot of things only after the police or his own attorney told it to him. It's entirely possible someone mentioned Avery's gun above the bed before Dassey ever said anything about it, just like happened with her being shot in the head, her body being found on Avery's property, the car, etc. I haven't read all of the interviews, but I would put good money on this being the case.
No, I do not think he is innocent simply because the cops planted evidence. I do, however, think it casts doubt on pretty much every single piece of evidence obtained in the case. If he was clearly guilty, even without the planted evidence, then why did the cops feel they needed to plant it? And once I acknowledge that the key and blood were likely planted, I can't take any piece of evidence as trustworthy. I just can't.
I don't feel sympathy for Steven Avery because I think he's a great guy. I feel sympathy for him because he spent 18 years in prison for something he didn't do and is likely sitting in prison again for something he didn't do. Simple as that. Burning his cat alive and running his cousin off the road, while deplorable behavior, does not make him a murderer and does not mean he should spend his life in prison. Our society doesn't work that way, and it's a good thing it doesn't.
Just FYI, but he didn't serve 18 years for something he didn't do. 6 of those years were from the assault on his cousin.
Avery was the last person she was ever seen with. Her car was found on his property. Her bones/belonging were round right outside his door in a burn barrel that multiple people saw him use on the night in question. Circumstantial evidence for sure, but we are talking about common sense; not whether a jury should convict.
(that is ignoring the DNA, key, blood, and nephews confession). Which, BTW, the little girl originally told authorities that Brendan was distraught over what he had seen or done with Avery. Though, months later she changed her story too.