Obviously there's no blood/DNA anywhere since the police forgot to plant it in the most damning places to make their case.
In any event, there was blood in the victim's vehicle where Dassey said Avery put her after the murder so there goes that idea that there was no blood found anywhere.
And no one really knows how she was killed except for Avery and Dassey. They could have had plastic on the floor to collect any blood when they shot her. All the questions are never answered in any case, let alone a murder case. There's still overwhelming evidence that points to Avery from the blocked phone calls, to the DNA evidence, to the body in the fire pit, to the vehicle at Avery's lot, to the circumstantial evidence and so on. None of us will ever know all the facts unless Avery finds God and confesses. But the guy in a psychopath. Even the woman that lived with him thinks he did it.