My only explanation for Kakashi obtaining the Mangekyou Sharingan is that he copied it from Itachi when they first encountered.Originally posted by: XanBcoo
He was referring to MANGEKYOU Sharingan. Now, I have not read the manga, but I was under the impression that Itachi found out about Kakashi's Mangekyou at the same time we did - that is, very recently.
There is no way he could have known Kakashi was the third person nearly 10 years prior. He was referring to someone else, making Kakashi the 4th user.
Kakashi didn't kill his best friend.
Which brings me to another point. I believe Itachi killed off his clan so no one could copy his Mangekyou.