Re: Why Rin got killed thread
Kakashi has no parents, so it's likely he took part in anbu root training, however, I think it's too hard to get out of, the rest of the possibilities seem vague IMO. Why would Rin be a spy. She showed no spy-like abilities, and healing isn't useful as a spy?? Jinchuriki no, rest seems weirder,
What is more, we have no real knowledge of how long Obito spend in that cave, but his hair grew really long. Why did Kakashi look exactly like he did, when Obito "died"? This is very confusing. Did Kakashi and Rin stay at the battlefield so long after? Perhaps they just had some B/C rank observation mission to keep an eye out for new enemies.
It would make sense if they had different observation posts, and thus Rin saw something, which gave her information of huge importance. She then sent the message with a summoning, or whatever method, she could have to do so back to Konoha. They found out, and Kakashi (who probably was nearby), came to help her, they run, he realize only choice is to kill her, since else they could find out, exactly, what she heard (which would be important if it was strategic plan or whatever). This also explains why backup came later.
In short, Rin obtained some important information, and thus they needed to capture her, to figure, what exactly it was, and thus torture etc would be used, and Kakashi killed her, for her sake.