How did he get into the CIA building without getting noticed?
And how did he leave, as he was in Noah's office, when Noah ordered everyone to close the building, and catch Bourne?
shareIt wasn't a CIA building. They were "using" a floor or two of an office building. He got in because just about everyone in the office left to follow Pam, just as he planned. The few that left were not expecting anyone to break in.
He got out by jamming or blocking the access codes for those still in the building. That one guy had to shoot the door to get out.
Si vis pacem, para bellum.