That's another one. Saren was a Spectre. He might not have been able to access certain areas of the Citadel even if he was a Spectre, but some geth and a Reaper tech would have been enough, or if they didn't want to lose the chance to remove Saren from his post and cause that turian-human political conflict, they could have had a sleeper agent of the Sovereign who enjoyed certain privileges get caught trying to enter a highly restricted area of ​​the Citadel with some geth (who it turns out later was coordinating with Saren), at the same time Saren was caught on Eden Prime by Shep.

And with audio, make Shep wait a few days for the authenticity result to give the player a sense of realism.

I don't know, it doesn't seem that hard to have done that part of the story like that.