For the people asking about his CCTV.
When it is switched on, the cameras at night will transmit infrared signals, when you watch the CCTV from the other house across the car park, that camera will pick up the infrared beams from bens cameras therefore illuminating that area around the side of his house.
When he switches off his cameras, what happens then is no infrared beam will be transmitted around his house at night, therefore the camera from No 23 wont have that area illuminated and that will then show that area in total darkness and won’t pick anything up from Bens house if he walked out and took Sarah’s body with him.
One can see on the CCTV footages the moment Bens cameras are turned off, from No23 that part of the car park at the side of Bens house goes into total darkness. It’s hard to spot but watch the CCTV,the night part of the car park 1 and you will see the side of his house go dark all of a sudden, you will also see what look like little spot lights where the cameras are on his house.
That’s why the cameras were turned off before he bolted from the house with her.