I Have recently had this email from a friend:
I have an interesting theory about River Song. I thing she's Prisoner Zero. In The Time of Angels, River and the army father guy have a private talk while in the cave thing and the army guy says, "he doesn't know yet does he? Who and what you are?" (the quote might be slightly wrong) so this implies that she is not human. Army guy also says "If he finds out he won't help us" (again, might be slightly wrong) which indicates that she is something evil, or at least, something that the Doctor thinks is evil at this point. At the end of the conversation River says "I'm not going back to prison" and in every episode so far (counting time of angels two parter as a single episode) there has been one of those time cracks that, in the first episode, was associated with prisoner zero. We already know that prisoner zero is a shape changer.
I have two further ideas. Either:
Prisoner Zero is not actually evil, the doctor just thinks it is hence the "he won't help us" and the fact that he supposedly later marries River. I mean, did Prisoner Zero actually kill someone when it was on earth? As far as I can remember it just put people into comas to use their shapes and threatened to kill people by using the police aliens to incinerate the earth.
I'm not quit sure about this idea though because it would imply that prisoner zero is not actually River but taking her form and keeping her body in a coma somewhere, and the army guy is in on it.
I think I just said my second idea - river being in a coma somewhere and prisoner zero is using her form and the army guy is in on it.
