The twist could also be his daughter's new dad being behind it all.
Or.
There is no one behind, it is a government experiment gone wrong, but no one dares to stop it because it gets rid of “the others”
Another thing. Imagine the power of planning and coverups it would take if you should do this game in real life?
No one questions the many people missing at once.
No one taking the dog for a walk at the bay and sees the many cars.
No one sneaking over to the island just because they are curious or want to have romantic camping.
Stalking all those people in that level of detailing is a huge effort in its self.
Imagen to mastermind all this. In real life OMG
I have trouble just getting my fictional character around my own story. And finding the right train when going to my job