Think again. Think about the "ransom note" and who might have written it and why. Also look at some of the reported statements by the parents that do not make sense, such as a reported statement by the father that he did not find his daughter on his first search of the basement. If he actually said that, I don't believe a father would ever have missed his daughter in the first search. That house isn't that big. OTOH, I saw the father on TV once and he struck me as a perfectly normal guy who would never harm his daughter. Nonetheless some of their statement don't make sense.
I'm thinking that some of these questions will be cleared up as we know the whole story. Off the top of my head, I'd say he knew Patsy Ramsey in some fashion.
I believe the house was built in the 1930's with many rooms in the basement. The house was huge.
Remember, though, he was thinking ALIVE. He was running around looking into rooms thinking she would be living, moving. He was probably not thinking about a body further back in a dark room. He probably wouldn't allow himself to go there. He did a very hurried check. The house was huge.
It sounds as if the DNA matched. Thank God he is caught.
I don't believe a father would ever have missed his daughter in the first search