So? They suspect CB of MM's murder based on their evidence, so why bother asking where it came from? That seems a rather naiive approach given that once they begin questioning they also have to grant the defence access to all their other evidence. What if the vid shows an unknown man, it's easy enough for CB to deny being that person, he could come up with any number of stories. But then, what if someone has captured a pic of him somewhere earlier that day wearing the same clothes? A lot harder to convince a judge of it being a coincidence then, and from what HCW has said, it seems like it might be something as simple as that is what they need to have confidence the charge will result in a prosecution.
Rubbish. Why would they HAVE to? You're just making stuff up, there's no law that says that's what they have to do.
And how do they check the true identity when there's no body? It doesn't need the McCanns to identify MM in a video or picture, anyone who knows what MM looks like could confirm that (as much as they could). But again, it's all hypothetical because even if there IS a video, you have no idea what it shows in order to be making assertions that the BKA would have had to told the parents about it.