That's so sad.
I understand the first thing they do is rule out the parents but good grief, at some point MOVE ON. If it wasn't the parents, you can't MAKE it have been them, even if you get them to confess. I think police do sometimes get too consumed with getting someone, anyone, and lose sight of the fact that if it's the wrong person, then they've accomplished nothing. I would think that if the parents "went from cooperating to not cooperating" it's because they know they didn't take their baby and they want the police to stop assing around and find the person who did. Every minute that goes by, the chances of finding that baby go down. As the parent of a missing child, that must drive you insane to know that they're hung up on you, YOU know you didn't do it, and what is happening to your child with the police are busy not looking for the person who took your baby.
I'm certainly not an expert or anything, but these parents don't send up any alarms with me and I am the most suspicious person in the world.
Several years ago the same thing happened with a couple in Florida (baby Sabrina) and the police said they had tapes of the two of them talking about doing coke and killing the baby. When they later released the tapes, there was nothing. Occasional sobs, no talking. They decided it was the parents. They neglected to tell the rest to mention that several other homes in their neighbor hood, all with infants, had been broken into in the past few weeks. When the police decide it's you, it's YOU. Ask the Ramseys.
I don't think all cops are bad, I have a great amount of respect for what they do. I think there are probably some jerks who just want to be right, but there are probably also a lot of good people who want to find out what happened to this baby and statistics and experience point to it most often being the parents.
Whatever happens, I do hope this baby is ok. It's so sad. I can't stop thinking about it. If it was the one night the dad worked late and the mom left the door unlocked (for him, I assume) my guess is that it's someone who knows them (I'm not a cop or doctor, I just play one on the interwebz).