I think that your observation about Dale not being reachable within key time stamps of the crime is justified and probably why he's considered a suspect, otherwise, assuming an ability to account for his whereabouts, he would probably not be one at this time.
I'm not sure what you mean by:
"...if Michelle was just abducted and planned to be held/killed later than any of the DNA left (hair, clothing, etc) do not produce evidence that a crime took place."
So suppose they found dried microscopic particles of blood belonging to MP in his van, would that not constitute evidence of foul play? Exactly when would he say that MP climbed in the back of his van and hurt herself? Or broke her fingernails there, or salivated on the floor of the van? Or lost a button there? Or otherwise when would he say that Michelle, for any reasons, had been in the back of his van? On top of it all, many such evidence may come with an ascertainable age ... No Jazz, I respectfully disagree there, no evidence in his truck, as no evidence at his condo are a huge problem for the police, THE most important task a DA needs to do is to place the accused at the crime scene at the time of the crime, having evidence of both, and although they can still get a conviction assuming significant corollary evidence, it would still be an uphill battle I'm afraid and the reason why DS has not been charged yet and not likely to be charged in the future unless they discover pertinent evidence that directly implicates him in the disappearance of Michelle ... like ... discovering where Michelle's body is and finding what is his there that should not have been. JMO
As for the phone not been discarded on the day of the crime, what would be the reason for Dale to hold on to it and the unbelievable danger that keeping it might have brought to him? If anything that would indicate someone other then Dale, someone that does not expect a search would involve his premises, his vehicle or anything of his, conversely Dale surely would have anticipated a search of everything that was his, so what does he do? ... Does he hide the phone somewhere to be retrieved later? Does he keep it in his pocket? In his van? For what reason? He gets caught with it he's guilty, end of story, why would he then keep it a nanosecond longer that he has to? There's basically nothing here indicating recklessness, obvious erratic emotional compulsions where the hiding of evidence is the issue, or anything that supports this perp being driven by anything else but an acute sense of caution and planning because he demonstrates to be through it all, as I said on many occasions, methodical and not necessarily someone like Dale who has a provable history of getting caught. What you have here is a statistically perfect candidate to have committed this crime but none of the brains with which this crime has apparently been carried out, unless of course he's not nearly as stupid as one might readily assume by what he has failed to accomplish in his life and all his shenanigans included therein, which remains not outside the realm of possibilities for what is not known is usually a lot more that what it is known. JMO