I've been thinking a lot about the timeline, AND the mention of a mysterious driver back from the beginning. Not being able to see the rest of the video (the part between 5:06 and 5:12 as well as a larger view of the area) makes it impossible for us armchair sleuthers to know anything more, but LE does.
William spoke to his wife about 5:00. At 5:06 a familiar SUV quickly backs up the driveway and parks, then leaves 6 minutes later at 5:12. Whatever happened occurred inside those 12 minutes.
Who in here thinks someone was in the house, called a friend to come over and they took William (alive) for some reason? Maybe they injured him, cleaned up quickly, then walked or carried him out and stuffed him in the auto. Whatever happened, someone had sense to turn off the oven (if it was off, do we know?), yet no one thought to make sure he had his wallet.