I completely understand how someone could think that was a possibility, but thinking something is possible and reality is 2 different things.
You can't just throw out a trial simply because you think something is possible, or could be possible. There is no proof that Manitowoc framed him, honestly what proof of a cover up besides possibilty warrants a retrial?
If the blood sample had shown EDTA's, like the blood from the vial did, then that would definitely be sketchy. If the bullet fragment found had not come from his gun, or her vehicle found on his property, or her phone had activity after she arrived, or her bones and apparel not found in his burn pile WITH burnt tire residue imbedded in them, or his DNA on the hood latch, or he hadn't acted very peculiar and anxious for her arrival the day she disappeared, or he had an alibi, or Brendan hadn't known details only a person involved would know.
At some point you have to look at what you think is possible and in what reality happened.