I think that there needs to be more tracking on home invasions, because they are becoming increasingly more prevalent and violent.
The problem is how, "Home Invasions" are documented, right now, the definition from the FBI, which tracks Home Invasions, it includes people known and unknown as the definition of "Home Invasion". This situation looks like a possible acquiescence home invasion, the perpetrators knew what they wanted, and knew how to get it. They knew that the home did not have a dog, security system, was isolated, and that the Father was not likely to have a gun handy.
Not unlike the situation with Elizabeth Smart. So, I would look at people who have been in that house in the last year. If the couple is reclusive, that would probably be not that many people.
I remember the issue with Elizabeth Smart kidnapping and Jon Benet murder, that the sheer amount of people who had been in the house or had access to the home, was astronomical.
That really made us think about who we let in our home, casually, and we changed after that. No one comes over any longer, unless it is for a specific purpose, we have no pictures out, doors to rooms are closed, and it is usually people we know personally, even for work in our home. And we do more maintenance ourselves.