The reason was very simple: It was because Luke and Selina's living habits were different.
Also, to prevent people from spying on his yard, and more than that, to guard against snipers, Luke had put up a wall about 1.8 meters tall, and had installed hidden cameras inside the wall carvings.
That way, gunmen couldn't fire directly at the house from the road, and if they lingered too long around the yard, they would be caught on the cameras which Luke set up.
These precautions were understandable for two police officers.
But Karen, who was too bored, told her husband that Luke had built the wall because he was hiding something.
Maybe these two people were making meth or even planting weed in the basement.
Thanks to the surveillance cameras, Luke had found this Karen wandering around his house a lot, so he, too, had monitored her in return.
