There are several reasons why I don't really think he did it, and many have already been stated. Some of my biggest are:
His truck - Everybody seems to agree that he loved it and wouldn't purposely damage it. It would make more sense to dump her body and leave with the truck. I can't see him purposely driving it to where it was found, but I also can't see him (or anybody else) pushing it down there and then running down to grab the keys from it.
Motive - A lot of people seem to think he may have done it because of a rumor that she was going to break up with him. I find it very hard to believe that someone who can make it through an amicable end to a marriage would become homicidal about a possible break up with someone he has probably not been seeing very long. (At least not long when compared to the time he was involved with his wife.)
Others - They were seen together not real long before she died and seemed to be getting along fine, she talked to her mother and nothing seemed to be bothering her, there were no signs of a struggle (I can't believe anyone just shoots a 'loved one' without things building up to that point somewhat.)
This one is probably the dumbest, but it's still something that came to my mind. Being a trained soldier, I can't see him shooting her 3 times. It seems like he'd know he could kill her with one shot, and would most likely do so if he was at all in control. If he wasn't in control, he would probably have emptied the gun.
If he had done it, I don't think he couldn't have gotten far enough away to be safe from police without being seen. Out in the country like that, most people would remember anyone they picked up. It's not like living near a major city where there are constantly cars going by from other cities/states, and I'm sure they don't have that many people going for leisurely walks out there either.
I know these are all generalizatins, and none of them prove he didn't do it. For now, though, they are enough to convince me that there was a 3rd person there, or more.
