Rin's death reasons?
Edit: Nevermind... I knew someone got there before me
Now I know I'm new and all and I could be so completely, PAINFULLY wrong in every land possible. When I was reading the manga for a second time a while ago, it struck my mind the idea of the sharingan.
When Kakashi was asked about how he got his Mangekyo Sharingan he answered that he had seen close friends die or he lost important people. Also, quoting from the Naruto Wiki (http://naruto.wikia.com/wiki/Mangeky%C5%8D_Sharingan), it says that 'Kakashi Hatake developed his own Mangekyō Sharingan during the time-skip. How he developed this is still unclear.'
Now, I know it may seem too stupid for Kakashi to kill Rin and I'm just being hopeful, but it does say that Mangekyo is only achievable through 'the trauma experienced from the death of the person closest to the Sharingan user.'
This also explains how Obito (Tobi) awakened Mangekyo Sharingan as you can see him WITNESSING Rin die, thus, traumatising him.
However, it may be a little more complex as you can see that both eyes share the same technique (AND VISION, http://www.narutobase.net/manga/Naruto/604/17) even though they have got different users. This suggests that Kakashi only awakened his Mangekyo because Obito awakened his Mangekyo, though he didn't realise it until much later (Maybe?).
I think there could be a possibility of this being explained in the next chapter, considering Kishi is the kind of person that would do this out of the blue.
Please don't hate I just wanted to share my revelation D: