I think the chances that they have Mickie getting into his truck under her own power and will are slim, with the "aggravated kidnapping" charge as well. If he hit her and it is on video, it may be apparent that it was not accidental, which could also account for the charge, even if she DID manage to get up and agree to get into his truck.
In any event, they seem to know she left the scene with him one way or another and is now believed to be deceased as a result of his actions.
As far as tying him to any of the missing girls or women near Spring, the first thing LE could do is find out where he was the dates they vanished, which should not be that difficult, if he was working the same job, on and offshore, at the time. For instance, where was he in April 2010, when Ali disappeared?