Clinton didn't need to be tipped off it may of been one of the five who had written notes on the side. When they wrote down their ideas they had no idea about 9/11 and that in time all of this would be looked at so when a commission is investigating they realize that they have to cover themselves.
Maybe they had no reason or excuse to go into the archives but knew Berger would have a perfect reason for being in there. The thing that needs to be known is who were the five????
Well that info will come out sooner or later