From a psychological standpoint, his answers, to me, seem like someone who is shocked and confused about the whole thing.
I think he was as informative as he could be. This isn't a boyfriend who was in her life for months and months. We are talking max 30-45 days. He went to school full time and had a busy social life. Really, I don't think he knew Casey all that well to that point. She may have "moved" in, but that doesn't mean he knew the details of everything in her life. 30 days is not a great length of time to learn about people's pasts, family members, etc. Everything in her life was a LIE. I think he was shocked and didn't know what to say. He seemed truthful and as upfront as he could be. I am sure while he was talking he is trying to process everything that is being said to him with things she said.
It is unnerving.
He has cooperated fully and continues to do so. We discussed his "interviews" at length and the fact that he has been staying out of the public spotlight. Who would want to be associated with Casey now? I can only imagine what he is feeling.