First of all, I am convinced that Kakashi does not seem to have a person who killed his partner. Secondly, Kakashi did not have to kill to get Mangekyou Obito, because he only had to experience death. In addition to a flashback that seems true enough.
Okay, so if you read the latest manga, you would understand why I brought back this thread. KAKASHI IS EVIL! so my guess was kind of right and i'm proud.