Sadly, this has happened before, and in many cases - cops follow what they think is their hottest lead and discount anything that contradicts their theory.
In this, they are only doing what other humans do, which is form a conclusion based on early evidence, and then it's harder for new evidence to get through. So they attended a course, for instance, in child abduction, in which they learned a parent is often involved. They meet DB, they don't like this plump lower-class woman who didn't initially tell them she was drunk that night and now they're off and running in this direction. Yes, cops fail to follow leads. This is why wealthy families hire private investigators. This is why many cases are never solved. This is why Jaycee Dugard was missing for many years. The leads were there, the cops didn't follow them - until two unusual female campus cops got an intuition about a guy that a lot of male cops and probation officers thought was just an okay guy. Those cops followed the lead and found Jaycee.
Don't get me wrong, I am not saying that there aren't a lot of hard-working LE on the case. But I believe that at the top, there is a mentality that they staked out early on a certain belief - including believing the husband without much verification - and they put manpower into the scenario against DB.