Who could the thief have been?
Orrery, as we have seen, had himself taken a packet of letters to Pope, which would be of course the letters from Pope to Swift.

The packet being sealed, Orrery did not know the contents, and Pope asserted that he had burnt it almost as soon as received.

It was, however, true that Swift had been in the habit of showing the originals to his friends, and some might possibly have been stolen or copied by designing people.

But this would not account for the publication of Swift's letters to Pope, which had never been out of Pope's possession.

As he had certainly been in possession of the other letters, it was easiest, even for himself, to suppose that some of his own servants were the guilty persons; his own honour being, of course, beyond question.
To meet these difficulties, Pope made great use of some stray phrases dropped by Swift in the decline of his memory, and set up a story of his having himself returned some letters to Swift, of which important fact all traces had disappeared.