I don’t think that MV being largely silent is in any way indicative of guilt - after all, he called the police himself and there is video of TG running away from the home.
But I think it indicates that he probably suspects what may have happened to him. MOO but my hunch is that this could be mental health or substance related. If someone has a mental break, or has gotten themselves in a situation where they are using substances in a dangerous way, a partner would likely know them well enough to know where they might go to ground or who might be involved in whatever happened next. That means they aren’t going to be out searching random culverts, because they know where they may be likely to run. If this was likely to be misadventure (running into fields and getting lost/injured) or foul play, a partner would probably be more likely to be making public appeals. JMO, of course.