after reading back some of the chapters this is some crap what i thought of lol

- Tobi is Shisui Uchiha who supposedly were killed by Itachi

- Shisui has magenkyou sharingan and shisui is the one that actually killed the entire uchiha clan and because people think he is dead the blame is on itachi

- shisui perhaps somehow help activate itachi's magenkyou sharingan for certain reason before the tragedy

- Itachi need to flee from the village because of the circumtances plus may be he is going after shisui (that's why he join akatsuki)

- itachi probably left sasuke in extreme psychological condition to make him become stronger later

- there is no way in such condition that itachi could explain to sasuke that he is not the one that killed their parent. He might just be unable to prevent Shisui from murdering the entire clan.

the reason that I say those is because

-tobi's saying  "the sharingan's true power, my power ... uchiha madara's power..." is too abstract

- itachi said before that if sasuke can activate magenkyou sharingan there will be three people that can use magenkyou sharingan

- there is no scene that actually show itachi murder his people I mean there is only scenes of him with the already dead bodies

- Itachi try to stop sasuke from entering the rooms were their parent is murdered but sasuke enter it nevertheless

- the memory in sasuke's brain is just the one planted by itachi using his sharingan and not the real one (the reason is probably to motivate him to become stronger)

- shisui is known to be one of the best of the Uchihas

OR

tobi is actually some one else who is not a an original sharingan user, he just got a sharingan planted in to his eye socket from an uchiha (perhaps madara?) just like kakashi.