: On top of the on top information, he would be somewhat aware inside the
: Cryptum and was meant to have access to the Domain, dwelling on the vast
: wisdom and knowledge left there by many generations of Forerunners, which
: would slowly calm his mind and "heal" him. This is evidenced by
: the Librarian mentioning in SpOps how he was meant to give the Janus Key
: to humanity and work with them to a better future.

: Instead, the Domain was destroyed by the firing of the Halos, which left him
: with nothing but 100,000 years of his own madness to dwell on.

I should say it was accidentally destroyed for reasons you should read on your own. ;)