How did Shisui get his Mangekyou Sharingan?

[Reynfall]

I think it has already been confirmed that you don't need to kill your best friend in order to get Mangekyou, you just need to experience emotional trauma on the same level.

 

[UncleSi]

Good Question? We will prolly never know...there is not enough info on the Uchiha that this manga loves to bring back up over and over again ...as somebody on here once said a lost Uchiha is a living Uchiha..I know the manga says he died but never explained how or where Itachi just says he died after giving him his left eye