One thing it didn't cover was whether the briefcase was returned
The briefcase was returned. I read a book about the operation years ago which included details of the testing done on the briefcase and contents after it was returned. IIRC one of the sealed letters, which had very carefully been folded only once, had two fold creases on the paper, so they knew it had been opened, read, refolded and resealed to make it look unopened.
HTH
EG