If this package was delivered by courier, and it was marked for Comey specifically, then the obvious person who opened it is McCabe. Now did McCabe contact Comey about it, and did Comey give him approval to open it? Perhaps. If he didn’t, and opened it without clearing it with Comey, then in my opinion, McCabe should be next in line to get the axe.
The obvious person to open it would have been Comey’s secretary who would have called Comey and then gone to McCabe. Lot of people in the mix at that point if they are hanging around the office at the time.