Where most people seemed to look at the later pages in this weeks chapter I took a look at a certain page:
Now I have been reading several theories over day, and in the end I got convinced that Rin was not a spy. The above page is from mangastream cause I tend to see their translations to be more correct. Anyway what is interesting is the difference in the translations. In mangareader they said: "Shit he got us", but the one from mangastream says: "Shit! He took her out". Also what comes after is interesting, they say "Just when we finally managed to get our hands on it" which is the same in both translations.
I am almost sure that the hidden mist village has acquired some sort of item or secret scroll, code whatever, it doesn't matter, the fact is that the mist shinobi says: "Just when we finally managed to get our hands on it".
This it must be an item of some sort. Then they kind of say that their plan failed because Kakashi killed her. So my guess is that Kakashi had to kill Rin because the mist shinobi would capture her and force to help them using "it". Whatever it is may be quite interesting as well. It also makes perfect sense for why kakashis only possibility was to kill her. Why they wanted her body is, however, hard to tell, but it's like Kakashi said:
Well read for yourself, these mist anbu are also known as body erasers, and he also says that a shinobi body carries many secrets. They never said they needed to erase the body, they said they needed to retrieve it. We also know they must erase the body the moment they get to it:
They also say they can't let the enemy get Rins body, which may just mean they don't want the enemy to erase it, cause their mission failed so they have to return with something, or they would probably be killed since it is the bloody mist.. It may be that her body holds a certain secret as well that can be used to use whatever it is they have.
Anyway not sure if anybody else have thought of this, but I haven't seen any, so I gave my opinion on it. Thanks for all the fine theories people made today, it helped me to think of this, lol. :o