Well i belive the one who knows everything is Konohamaru !
Orochimaru knew Hiruzen had a Son and Oro will go to konahamaru to find top secret files that Hiruzen tell Konohamaru to hidefrom everyone
The files contains the plans for the uchiha clan massacre !
What do you think ?
Note: Dont say its impossible as long as Tobi is Obito everyting its possible !