I agree, by all accounts his parents were doing everything in their power to help him and hold him accountable. I suspect calling police over the stolen cell phone when he was a teenager was not easy. Frankly, even knowing what he did, I look at him and have difficulty reconciling who he appears to be (polite, well mannered) with what he did. I suspect his parents were the same and hoping for the best, while accepting his idiosyncrasies (autism, ocd, germaphobe, etc.).
Based on where he was earlier in his life, working through problems, getting his life on track, earning a masters, being accepted into a Ph.D. program with a teaching assistantship (this is not an easy feat, very competitive), his parents must have been very proud and thought they rounded the corner!!
Also, for dad to still hold onto the possibility of his innocence isn't surprising. His college professor/advisor did too.