Did the MSP rifle through all of Venus' belongings, take her cellphone, her keys, and all the "notes" that she made? Venus' father said he found a "note" written by Venus accusing "someone" of molesting her children. Did the MSP find that note, and did they convey that information to him, or did he find it after they left the house to investigate Doug?
I can't say it enough. When doing investigations like this where the POI has an alibi, you have to GO BACK and start with the people who were the last to see her alive. There was bad blood between the father and Doug before she disappeared. Doug accused the guy of some type of crime, which Venus wrote about. That is a given. Of course he is going to say Doug did it, that he must have kidnapped her in her pajamas when she was at the mailbox, even though the father didn't see anything. Law enforcement is investigating this crime, not the father.
They should have taken her phone to see her message traffic. Then they should take her keys to find out what each key was resolved for, what vehicles, residences, PO Boxes if any, safe-deposit boxes. Then they should have went to where she was sleeping and taken everything she wrote about because that is also evidence. When people are writing things down, they want something tangible left behind and that is why Venus did that. The father should have found nothing after the police left the scene to look for Venus.
See, if Doug has an alibi, that means someone else did the crime. Doug may be complicit in that too, but he is a jar-head and I don't think he was smart enough to plan something like this out with someone else helping him. The guy was a ex-Marine jar-head truckdriver, not a Ph.D.