Hey guys, I'm new here, so hopefully this being my first post isn't an infraction of sorts
But anyway, I am thinking that Moriarty showing up on the cameras at the end is caused by one of several possibilities.
A. It's caused by someone who is NOT Moriarty
Sherlock? When he shoots CAM, it seems as if it is because he was outwitted by him. However, Sherlock might have planned this beforehand and used the distraction to be kept in England. Irene Adler? Giving Sherlock a hand after he saved her life? Possible, but not probably in my opinion, as I doubt she would have suddenly become a "good guy", which she would need to be in future episodes after we find out its her. Someone related to Moriarty in some way, or a future villain. This seems like the most reasonable solution. Its someone who wants to distract the country with Moriarty while working on another purpose. Others. It would have to be someone tech-savvy, which narrows the list down drastically.
B. It's Moriarty
Moriarty never died from the gunshot wound. Highly, highly, doubt this. Sherlock, while destroying his network, would definitely have made sure that Moriarty was dead. The person on the rooftop wasn't Moriarty. Moriarty was able to find a close lookalike of Sherlock, so why couldn't he find one of himself? But this theory seems too farfetched, albeit more credible than Moriarty surviving the rooftop. There is little reason that Moriarty would send some lookalike of himself to confront Sherlock before his intended suicide. Of course, Moriarty could be some completely different person from Richard Brook, and he was an actor all the time. But this would make the brilliant acting of Andrew Scott seem like a waste.
These are just a few thoughts of mine wanted to get them off my mind.