I try not to weigh in very often on this subject because my views aren't always popular, but hear me out.
As far as MP's actions, think about it this way. Their marriage has been on the rocks and they have not been getting along. GP called 911 several times during arguments. What if she was calling 911 to get back at MP? What if she was angry and he knew it and she wanted to punish him? What if he thought all along that she was trying to set him up for something? What if he has thought all along that she left to hurt him and make him look bad? What if he was concerned that she had planted evidence to get him in trouble with the law? Could that be a reason that he "lawyered up"... to protect himself? Maybe he didn't look for her because the whole time he truly believed that she had taken off because the idea that she had been in an accident or that something had happened to her was way too coincidental.
If I thought that my spouse was trying to set me up, if I found out that they had given money and other belongings to other people to hold, if I knew that I had screwed up and they had every reason to want to make me suffer, you can bet that I would do what it takes to protect myself. But I am a woman, so no one would question that.
I am not saying any of this to make Gail look bad in any way, because I know that if I found out what she found out... I would be looking to make my husband pay. I guess that is what I have always felt, so finding out that she was in an accident all along really blew me out of the water. I am only saying this because MP's actions after she left have been holding a lot of weight in people thinking that he did something to her. I think his actions make sense from that perspective. If I thought someone was trying to set me up or take off with my kids, I would file every legal paper I could, I would hire lawyers and I would do what it took to protect myself.
ETA: making sensing does not mean that the actions were ok, it just means that they make sense. I hope THAT makes sense.
My personal opinion is that this was a tragic accident. I want there to be a thorough and conclusive investigation so that we all know as much of the truth as we can, no matter what it is. I do hope that those who feel that his actions were deplorable can be open to a different perspective so that maybe they can at least make a little more sense. People make mistakes, people have affairs and marriages end. That doesn't mean someone was murdered.