You have an eyewitness with no rational motivation for lying telling the inquest that he witnessed the two in a bearhug for an extended period, then the male let go of the female who begin descending without movement.
Add this to the computer, the request regarding the insurance, and the deal with removing the flowers from the grave, and you've got a control freak manipulating events because doing so is something he does well and enjoys getting away with. Not an unheard of situation, in any number of crime scenarios.
IMO this was no accident, and no physiological reaction or diving-related explanation exhibited by the husband has suggested otherwise. The guy is getting away with murder because up until how he is correct - there is insufficient evidence to convict him. He has, in fact, succeeded in controlling the situation ultimately. What a rush it must be for him. The thing about cutting flowers off the grave with boltcutters may be the ultimate act of vindictive one-upmanship to her family. "I'll show you"; "you are not going to have the last word here, I am." He's a control freak. The thing with sending the Christmas card photo of himself to the bride's best friend is another example of gloating, of taunting. "Run, run, run as fast as you can: can't catch me, I'm the Gingerbread Man". Control can be a pretty heady phenomenon...particularly if you've convinced yourself that you're smarter than the average person, and able to get away with things that less-intelligent people can't figure out.
He'll reap what he's sown one day one place, but probably not until he's ruined a few more lives in the process... I doubt that any of the inqueries will be able to produce 'evidence beyond a doubt' of his guilt. He's an actor, and a con man, and a manipulator par excellance. And he will continue to behave in such a manner that he controls what happens, and that he has the last word.
Its a pretty sad situation, all around.
Doc