I would say from the slightly jerky nature of the movement that the video has been speeded up.
Two options occur to me:
1. If you wanted just to show Leah, why not show her in real time?
If you wanted to show her AND the person behind, you could edit out the pause (as they did recently with Libby case). However, then people would ask 'what happened in the gap'? And it would be V clear that they are looking for the person behind.
The only way to 'accidentally' include that person behind, AND show Leah, without people turning off assuming nothing is going to happen, is to speed up the footage.
2. UNLESS (and i don't know how CCTV of this nature works?) it's a series of still shots, captured, eg, every other second, so the only way to 'animate' it is as a speeded up video.