Since LE didn't secure the lab building for several days, the defense is going to jump on that bandwagon and say that the evidence was contaminated. Of course, I don't think it's going to fly, but - I do think that his father wanted to get him away and talk to him about what was to come and how to handle it.
The defense *might* be able to get some things thrown out, but DNA evidence of both perpetrator and victim on each other's clothing and/or bodies is pretty much impossible to get out of. If they threw everything else out and only considered evidence reportedly found on and around the body, he will still be convicted.
Remember, her body was hidden behind a wall in a crawlspace rather than out in the open where he could plausibly say he was before the crime. There's just no way that particular evidence would be excluded. It also happens to be the evidence that is the most damning for him.