Hopefully this is some evidence to further strengthen my theory of the sharingan/mangekyo sharingan.
Here is a pic of Itachi's eyes after he supposedly killed his best friend; We also assume this is how he obtained his MS since it's the first time we see it:
Now here is a pic after he supposedly slaughtered the Uchiha clan:
As you can see, compared to the first pic, his eyes in the second picture look different. You can almost say his eyes are complete, since the first pic it looks like the mangekyo sharingan was still developing. Seems like just kiilling a friend wasn't enough, so to make his eyes more powerful Itachi wiped out the rest of the Uchiha clan.
Seems like with this my theory seems even more feasible.